TED2014
Ed Yong: Zombie roaches and other parasite tales
Filmed:
Readability: 4.9
1,829,488 views
In this fascinating, hilarious and ever-so-slightly creepy talk, science writer Ed Yong tells the story of his favorite parasites -- animals and organisms that live on the bodies (and brains!) of other organisms, causing them to do their bidding. Do humans have them too? Maybe ...
Ed Yong - Science writer
Ed Yong blogs with a mission: to ignite excitement for science in everyone, regardless of their education or background. Full bio
Ed Yong blogs with a mission: to ignite excitement for science in everyone, regardless of their education or background. Full bio
Double-click the English transcript below to play the video.
00:12
A herd of wildebeests, a shoal of fish,
0
645
2551
00:15
a flock of birds.
1
3196
1629
00:16
Many animals gather in large groups
2
4825
2068
00:18
that are among the most wonderful spectacles
3
6893
1986
00:20
in the natural world.
4
8879
1718
00:22
But why do these groups form?
5
10597
2724
00:25
The common answers include things like
6
13321
1637
00:26
seeking safety in numbers or hunting in packs
7
14958
2966
00:29
or gathering to mate or breed,
8
17924
2496
00:32
and all of these explanations,
9
20420
1668
00:34
while often true,
10
22088
1237
00:35
make a huge assumption about animal behavior,
11
23325
3043
00:38
that the animals are in control of their own actions,
12
26368
3177
00:41
that they are in charge of their bodies.
13
29545
2251
00:43
And that is often not the case.
14
31796
3427
00:47
This is Artemia, a brine shrimp.
15
35223
2924
00:50
You probably know it better as a sea monkey.
16
38147
2764
00:52
It's small, and it typically lives alone,
17
40911
1995
00:54
but it can gather in these large red swarms
18
42906
3077
00:57
that span for meters,
19
45983
2247
01:00
and these form because of a parasite.
20
48230
3090
01:03
These shrimp are infected with a tapeworm.
21
51320
2686
01:06
A tapeworm is effectively a long, living gut
22
54006
2251
01:08
with genitals at one end and
a hooked mouth at the other.
a hooked mouth at the other.
23
56257
2888
01:11
As a freelance journalist, I sympathize.
24
59145
2535
01:13
(Laughter)
25
61680
2155
01:15
The tapeworm drains nutrients from Artemia's body,
26
63835
2908
01:18
but it also does other things.
27
66743
2077
01:20
It castrates them,
28
68820
1620
01:22
it changes their color from transparent to bright red,
29
70440
4718
01:27
it makes them live longer,
30
75158
1516
01:28
and as biologist Nicolas Rode has found,
31
76674
2357
01:31
it makes them swim in groups.
32
79031
3359
01:34
Why? Because the tapeworm,
like many other parasites,
like many other parasites,
33
82390
3452
01:37
has a complicated life cycle
34
85842
1581
01:39
involving many different hosts.
35
87423
2264
01:41
The shrimp are just one step on its journey.
36
89687
2404
01:44
Its ultimate destination is this,
37
92091
2612
01:46
the greater flamingo.
38
94703
1947
01:48
Only in a flamingo can the tapeworm reproduce,
39
96650
3025
01:51
so to get there, it manipulates its shrimp hosts
40
99675
3289
01:54
into forming these conspicuous colored swarms
41
102964
3091
01:58
that are easier for a flamingo to spot
42
106055
2717
02:00
and to devour,
43
108772
1559
02:02
and that is the secret of the Artemia swarm.
44
110331
2932
02:05
They aren't sociable through their own volition,
45
113263
2163
02:07
but because they are being controlled.
46
115426
2076
02:09
It's not safety in numbers.
47
117502
1694
02:11
It's actually the exact opposite.
48
119196
1859
02:13
The tapeworm hijacks their brains and their bodies,
49
121055
3041
02:16
turning them into vehicles
50
124096
1396
02:17
for getting itself into a flamingo.
51
125492
3967
02:21
And here is another example
52
129459
1430
02:22
of a parasitic manipulation.
53
130889
2526
02:25
This is a suicidal cricket.
54
133415
2976
02:28
This cricket swallowed the
larvae of a Gordian worm,
larvae of a Gordian worm,
55
136391
3304
02:31
or horsehair worm.
56
139695
1893
02:33
The worm grew to adult size within it,
57
141588
2156
02:35
but it needs to get into water in order to mate,
58
143744
3038
02:38
and it does that by releasing proteins
59
146782
2218
02:41
that addle the cricket's brain,
60
149000
2188
02:43
causing it to behave erratically.
61
151188
2164
02:45
When the cricket nears a body of water,
62
153352
1955
02:47
such as this swimming pool,
63
155307
1619
02:48
it jumps in and drowns,
64
156926
2257
02:51
and the worm wriggles out
65
159183
1725
02:52
of its suicidal corpse.
66
160908
3856
02:56
Crickets are really roomy. Who knew?
67
164764
3603
03:00
The tapeworm and the Gordian worm are not alone.
68
168367
3215
03:03
They are part of an entire cavalcade
69
171582
1720
03:05
of mind-controlling parasites,
70
173302
2077
03:07
of fungi, viruses, and worms and insects and more
71
175379
3949
03:11
that all specialize in subverting and overriding
72
179328
2573
03:13
the wills of their hosts.
73
181901
2209
03:16
Now, I first learned about this way of life
74
184110
1737
03:17
through David Attenborough's "Trials of Life"
75
185847
2493
03:20
about 20 years ago,
76
188340
1722
03:22
and then later through a wonderful book called
77
190062
1702
03:23
"Parasite Rex" by my friend Carl Zimmer.
78
191764
2674
03:26
And I've been writing about
these creatures ever since.
these creatures ever since.
79
194438
2143
03:28
Few topics in biology enthrall me more.
80
196581
2811
03:31
It's like the parasites have subverted my own brain.
81
199392
3706
03:35
Because after all, they are always compelling
82
203098
2611
03:37
and they are delightfully macabre.
83
205709
1288
03:38
When you write about parasites,
84
206997
1392
03:40
your lexicon swells with phrases like
85
208389
2084
03:42
"devoured alive" and "bursts out of its body."
86
210473
3046
03:45
(Laughter)
87
213519
1237
03:46
But there's more to it than that.
88
214756
1540
03:48
I'm a writer, and fellow writers in the audience
89
216296
2102
03:50
will know that we love stories.
90
218398
2709
03:53
Parasites invite us to resist the allure
91
221107
2393
03:55
of obvious stories.
92
223500
1850
03:57
Their world is one of plot twists
93
225350
2310
03:59
and unexpected explanations.
94
227660
3607
04:03
Why, for example,
95
231267
1496
04:04
does this caterpillar
96
232763
2178
04:06
start violently thrashing about
97
234941
1974
04:08
when another insect gets close to it
98
236915
1668
04:10
and those white cocoons that it seems
99
238583
2257
04:12
to be standing guard over?
100
240840
1438
04:14
Is it maybe protecting its siblings?
101
242278
3096
04:17
No.
102
245374
1449
04:18
This caterpillar was attacked
103
246823
1457
04:20
by a parasitic wasp which laid eggs inside it.
104
248280
3219
04:23
The eggs hatched and the young wasps
105
251499
1434
04:24
devoured the caterpillar alive
106
252933
1314
04:26
before bursting out of its body.
107
254247
1671
04:27
See what I mean?
108
255918
2275
04:30
Now, the caterpillar didn't die.
109
258193
2838
04:33
Some of the wasps seemed to stay behind
110
261031
2585
04:35
and controlled it into defending their siblings
111
263616
3337
04:38
which are metamorphosing
112
266953
1634
04:40
into adults within those cocoons.
113
268587
2020
04:42
This caterpillar is a head-banging
zombie bodyguard
zombie bodyguard
114
270607
3539
04:46
defending the offspring
115
274146
1301
04:47
of the creature that killed it.
116
275447
2222
04:49
(Applause)
117
277669
3866
04:53
We have a lot to get through.
I only have 13 minutes. (Laughter)
I only have 13 minutes. (Laughter)
118
281535
4295
04:57
Now, some of you are probably just
119
285830
1811
04:59
desperately clawing for some solace
120
287641
2218
05:01
in the idea that these things are oddities
121
289859
2260
05:04
of the natural world, that they are outliers,
122
292119
1931
05:06
and that point of view is understandable,
123
294050
1820
05:07
because by their nature, parasites are quite small
124
295870
2378
05:10
and they spend a lot of their time
125
298248
1340
05:11
inside the bodies of other things.
126
299588
2954
05:14
They're easy to overlook,
127
302542
1771
05:16
but that doesn't mean that they aren't important.
128
304313
2585
05:18
A few years back, a man called Kevin Lafferty
129
306898
2205
05:21
took a group of scientists
into three Californian estuaries
into three Californian estuaries
130
309103
3369
05:24
and they pretty much weighed and dissected
131
312472
1748
05:26
and recorded everything they could find,
132
314220
1995
05:28
and what they found
133
316215
1228
05:29
were parasites in extreme abundance.
134
317443
3216
05:32
Especially common were trematodes,
135
320659
2044
05:34
tiny worms that specialize in castrating their hosts
136
322703
2650
05:37
like this unfortunate snail.
137
325353
2546
05:39
Now, a single trematode is tiny, microscopic,
138
327899
2889
05:42
but collectively they weighed as much
139
330788
1799
05:44
as all the fish in the estuaries
140
332587
2186
05:46
and three to nine times more than all the birds.
141
334773
3707
05:50
And remember the Gordian worm that I showed you,
142
338480
1994
05:52
the cricket thing?
143
340474
1388
05:53
One Japanese scientist called Takuya Sato
144
341862
2553
05:56
found that in one stream,
145
344415
1696
05:58
these things drive so many crickets
146
346111
1971
06:00
and grasshoppers into the water
147
348082
1299
06:01
that the drowned insects
148
349381
1309
06:02
make up some 60 percent of the diet of local trout.
149
350690
4304
06:06
Manipulation is not an oddity.
150
354994
2934
06:09
It is a critical and common part
151
357928
2120
06:12
of the world around us,
152
360048
1891
06:13
and scientists have now found
153
361939
1521
06:15
hundreds of examples of such manipulators,
154
363460
2482
06:17
and more excitingly, they're starting to understand
155
365942
2437
06:20
exactly how these creatures control their hosts.
156
368379
4058
06:24
And this is one of my favorite examples.
157
372437
2524
06:26
This is Ampulex compressa,
158
374961
2457
06:29
the emerald cockroach wasp,
159
377418
2224
06:31
and it is a truth universally acknowledged
160
379642
2294
06:33
that an emerald cockroach wasp in possession
161
381936
1643
06:35
of some fertilized eggs
162
383579
1796
06:37
must be in want of a cockroach.
163
385375
2466
06:39
When she finds one,
164
387841
1200
06:41
she stabs it with a stinger
165
389041
2211
06:43
that is also a sense organ.
166
391252
1449
06:44
This discovery came out three weeks ago.
167
392701
2671
06:47
She stabs it with a stinger that is a sense organ
168
395372
2305
06:49
equipped with small sensory bumps
169
397677
1794
06:51
that allow her to feel the distinctive texture
170
399471
2555
06:54
of a roach's brain.
171
402026
2107
06:56
So like a person blindly rooting about in a bag,
172
404133
3041
06:59
she finds the brain, and she injects it with venom
173
407174
2477
07:01
into two very specific clusters of neurons.
174
409651
4201
07:05
Israeli scientists Frederic Libersat and Ram Gal
175
413852
3083
07:08
found that the venom is a
very specific chemical weapon.
very specific chemical weapon.
176
416935
3725
07:12
It doesn't kill the roach, nor does it sedate it.
177
420660
2544
07:15
The roach could walk away
178
423204
2127
07:17
or fly or run if it chose to,
179
425331
3025
07:20
but it doesn't choose to,
180
428356
1875
07:22
because the venom nixes its motivation to walk,
181
430231
3380
07:25
and only that.
182
433611
1114
07:26
The wasp basically un-checks
the escape-from-danger box
the escape-from-danger box
183
434725
3706
07:30
in the roach's operating system,
184
438431
1840
07:32
allowing her to lead her helpless victim
185
440271
3233
07:35
back to her lair by its antennae
186
443504
2111
07:37
like a person walking a dog.
187
445615
2639
07:40
And once there, she lays an egg on it,
188
448254
1677
07:41
egg hatches, devoured alive, bursts out of body,
189
449931
2276
07:44
yadda yadda yadda, you know the drill.
190
452207
2189
07:46
(Laughter) (Applause)
191
454396
3230
07:49
Now I would argue that, once stung,
192
457626
2880
07:52
the cockroach isn't a roach anymore.
193
460506
2005
07:54
It's more of an extension of the wasp,
194
462511
2350
07:56
just like the cricket was an
extension of the Gordian worm.
extension of the Gordian worm.
195
464861
2843
07:59
These hosts won't get to survive or reproduce.
196
467719
2800
08:02
They have as much control over their own fates
197
470519
1799
08:04
as my car.
198
472318
1784
08:06
Once the parasites get in,
199
474102
1500
08:07
the hosts don't get a say.
200
475602
2565
08:10
Now humans, of course,
201
478167
1314
08:11
are no stranger to manipulation.
202
479481
2032
08:13
We take drugs to shift the chemistries of our brains
203
481513
2360
08:15
and to change our moods,
204
483873
1131
08:17
and what are arguments or advertising or big ideas
205
485004
4020
08:21
if not an attempt to influence someone else's mind?
206
489024
3703
08:24
But our attempts at doing this
207
492727
1527
08:26
are crude and blundering compared
208
494254
1778
08:28
to the fine-grained specificity of the parasites.
209
496032
3095
08:31
Don Draper only wishes he was as elegant
210
499127
2392
08:33
and precise as the emerald cockroach wasp.
211
501519
4960
08:38
Now, I think this is part of what makes parasites
212
506479
3740
08:42
so sinister and so compelling.
213
510219
2786
08:45
We place such a premium on our free will
214
513005
2622
08:47
and our independence
215
515627
1261
08:48
that the prospect of losing those qualities
216
516888
1581
08:50
to forces unseen
217
518469
1278
08:51
informs many of our deepest societal fears.
218
519747
3168
08:54
Orwellian dystopias and shadowy cabals
219
522915
2453
08:57
and mind-controlling supervillains --
220
525368
1854
08:59
these are tropes that fill our darkest fiction,
221
527222
3028
09:02
but in nature, they happen all the time.
222
530250
4798
09:07
Which leads me to an obvious
223
535048
2632
09:09
and disquieting question:
224
537680
2300
09:11
Are there dark, sinister parasites
225
539980
1723
09:13
that are influencing our behavior
226
541703
1956
09:15
without us knowing about it,
227
543659
1575
09:17
besides the NSA?
228
545234
2819
09:20
If there are any —
229
548053
1307
09:21
(Laughter) (Applause)
230
549360
3966
09:25
I've got a red dot on my forehead now, don't I?
231
553326
2322
09:27
(Laughter)
232
555648
2527
09:30
If there are any, this is a good candidate for them.
233
558175
2954
09:33
This is Toxoplasma gondii, or Toxo, for short,
234
561129
3278
09:36
because the terrifying creature
235
564407
1589
09:37
always deserves a cute nickname.
236
565996
2210
09:40
Toxo infects mammals,
237
568206
2282
09:42
a wide variety of mammals,
238
570488
1478
09:43
but it can only sexually reproduce in a cat.
239
571966
3081
09:47
And scientists like Joanne Webster have shown that
240
575047
2761
09:49
if Toxo gets into a rat or a mouse,
241
577808
2193
09:52
it turns the rodent into a cat-seeking missile.
242
580001
3472
09:55
If the infected rat smells the delightful odor
243
583473
3076
09:58
of cat piss,
244
586549
1224
09:59
it runs towards the source of the smell
245
587773
2720
10:02
rather than the more sensible direction of away.
246
590493
3919
10:06
The cat eats the rat. Toxo gets to have sex.
247
594412
2535
10:08
It's a classic tale of Eat, Prey, Love.
248
596947
2872
10:11
(Laughter) (Applause)
249
599819
4668
10:19
You're very charitable, generous people.
250
607512
3202
10:22
Hi, Elizabeth, I loved your talk.
251
610714
2585
10:25
How does the parasite control its host
252
613299
3368
10:28
in this way?
253
616667
1204
10:29
We don't really know.
254
617871
1326
10:31
We know that Toxo releases an enzyme
255
619197
1688
10:32
that makes dopamine, a substance involved
256
620885
1992
10:34
in reward and motivation.
257
622877
1813
10:36
We know it targets certain parts of a rodent's brain,
258
624690
2431
10:39
including those involved in sexual arousal.
259
627121
2465
10:41
But how those puzzle pieces fit together
260
629586
2201
10:43
is not immediately clear.
261
631787
1844
10:45
What is clear is that this thing
262
633631
2296
10:47
is a single cell.
263
635927
1392
10:49
This has no nervous system.
264
637319
1370
10:50
It has no consciousness.
265
638689
1132
10:51
It doesn't even have a body.
266
639821
1301
10:53
But it's manipulating a mammal?
267
641122
2624
10:55
We are mammals.
268
643746
1426
10:57
We are more intelligent than a mere rat, to be sure,
269
645172
2434
10:59
but our brains have the same basic structure,
270
647606
2524
11:02
the same types of cells,
271
650130
1393
11:03
the same chemicals running through them,
272
651523
1588
11:05
and the same parasites.
273
653111
2319
11:07
Estimates vary a lot, but some figures suggest
274
655430
2348
11:09
that one in three people around the world
275
657778
2360
11:12
have Toxo in their brains.
276
660138
1713
11:13
Now typically, this doesn't lead to any overt illness.
277
661851
3488
11:17
The parasite holds up in a dormant state
278
665339
1878
11:19
for a long period of time.
279
667217
2183
11:21
But there's some evidence that those people
280
669400
2039
11:23
who are carriers score slightly differently
281
671439
3034
11:26
on personality questionnaires than other people,
282
674473
2729
11:29
that they have a slightly
higher risk of car accidents,
higher risk of car accidents,
283
677202
2484
11:31
and there's some evidence
that people with schizophrenia
that people with schizophrenia
284
679686
2603
11:34
are more likely to be infected.
285
682289
2546
11:36
Now, I think this evidence is still inconclusive,
286
684835
2183
11:39
and even among Toxo researchers,
287
687018
1911
11:40
opinion is divided as to whether the parasite
288
688929
2440
11:43
is truly influencing our behavior.
289
691369
2385
11:45
But given the widespread
nature of such manipulations,
nature of such manipulations,
290
693754
2659
11:48
it would be completely implausible
291
696413
1845
11:50
for humans to be the only species
292
698258
1649
11:51
that weren't similarly affected.
293
699907
2946
11:54
And I think that this capacity to constantly
294
702853
4393
11:59
subvert our way of thinking about the world
295
707246
2867
12:02
makes parasites amazing.
296
710113
1547
12:03
They're constantly inviting us to
look at the natural world sideways,
look at the natural world sideways,
297
711660
3209
12:06
and to ask if the behaviors we're seeing,
298
714869
2171
12:09
whether they're simple and obvious
299
717040
1487
12:10
or baffling and puzzling,
300
718527
1533
12:12
are not the results of individuals
301
720060
2086
12:14
acting through their own accord
302
722146
1853
12:15
but because they are being bent
303
723999
1809
12:17
to the control of something else.
304
725808
2670
12:20
And while that idea may be disquieting,
305
728478
2040
12:22
and while parasites' habits may be very grisly,
306
730518
2923
12:25
I think that ability to surprise us
307
733441
1792
12:27
makes them as wonderful and as charismatic
308
735233
3175
12:30
as any panda or butterfly or dolphin.
309
738408
3364
12:33
At the end of "On the Origin of Species,"
310
741772
2219
12:35
Charles Darwin writes about the grandeur of life,
311
743991
2989
12:38
and of endless forms most beautiful
312
746980
2653
12:41
and most wonderful,
313
749633
1432
12:43
and I like to think he could easily have been talking
314
751065
2579
12:45
about a tapeworm that makes shrimp sociable
315
753644
3180
12:48
or a wasp that takes cockroaches for walks.
316
756824
3249
12:52
But perhaps, that's just a parasite talking.
317
760073
3149
12:55
Thank you.
318
763222
1731
12:56
(Applause)
319
764953
4000
ABOUT THE SPEAKER
Ed Yong - Science writerEd Yong blogs with a mission: to ignite excitement for science in everyone, regardless of their education or background.
Why you should listen
Whether he's exploring a possible resurrection for extinct mouth-birthing amphibians or skewering media misunderstandings of hyped hormones like oxytocin, Ed Yong has a gift for illuminating the beauty (or controversy) in difficult and complex topics.
The award-winning blog Not Exactly Rocket Science (hosted by National Geographic) is the epicenter of Yong’s formidable web and social media presence. In its posts, he tackles the hottest and most bizarre topics in science journalism. As he says, “The only one that matters to me, as far as my blog is concerned, is that something interests me. That is, excites or inspires or amuses me.” When not blogging, he also finds time to contribute to Nature, Wired, Scientific American and many other web and print outlets.
He is also the author of the book I Contain Multitudes: The Microbes Within Us and a Grander View of Life.
Ed Yong | Speaker | TED.com