The Bug Geek

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Poop, not parasites

So a very cool bug photo has been circulating on the web: I’ve seen it on Tumblr, Facebook, Pinterest and Twitter. It’s a pretty darn great photo:

Photo of a Cereal Leaf Beetle Larva, by Giles San Martin, used under a Creative Commons License.

Photo of a Cereal Leaf Beetle Larva, by Giles San Martin, used under a Creative Commons License.

Let’s zoom in on that a little, shall we?


Well, my goodness. That’s really something, isn’t it? Here’s the accompanying story circulating on the web:

This is a juvenile form of the Cereal leaf beetle (Oulema melanopus) after being parasitized by Tetrastichus julis, a parasitoid wasp which lays its eggs inside the larva of the beetle. They eggs hatch within the larvae and begin to feed while it is still alive, before they burst out and kill it.These parasites are often used as a biological control, as the Cereal leaf beetle is considered a pest and regularly feeds on crops.

Well, now, that is REALLY something isn’t it? Parasites are so freaking cool.

The problem is, the pairing of this particular image with this particular caption has lead to some confusion. 

While the species identities are correct, and the stated relationship between the two is correct, the caption seems to imply that the skin of the poor beetle larva is stretched shiny-tight and close to bursting from a insanely huge parasite load (indeed, this is how the interwebz has been interpreting it).

This interpretation is only a little bit correct.

The beetle IS parasitized – by one parasite. Just one. 

The rest of that squirmy-looking mass on the back of the beetle is a perfectly normal thing (well, if you’re a leaf beetle anyways): it’s a fecal shield. Yes, fecal shield. As in, “poop”.

Many, many Chrysomelids (leaf beetles) create fecal shields, depositing their feces on their backs. It’s so prevalent, in fact, that the study of fecal shields warrants its own term, apparently. From the section in Caroline Chaboo’s book chapter on Chrysomelid defences entitled, “Fececology” (ha!):

The [Chrysomelid] subfamily Cassidinae has ~3,000 species whose larvae carry a mobile shield made of dried feces, attached to paired processes at their hind end, and held over the body like an umbrella. This shield may be held flat on the dorsum or elevated to hit an attacker. In two other leaf beetle subgroups, the subfamily Criocerinae (~1,400 species) and in some members of the subfamily Galerucinae (~14,000 species) the fecal material is simply piled directly onto the back of the animals, with some falling off as the animal moves around but regularly replenished to maintain coverage of the exposed dorsal surface (Fig. 2b, c). In Chrysomelinae leaf beetles (~4,000 species), the mothers take time to build a fecal case entirely around every single egg.

Compare the photo above with this one showing the fecal shield of a Criocerine Chrysomelid, Lilioceris lilii:

Photo by Luis Sanchez, used under a Creative Commons License.

Photo by Luis Sanchez, used under a Creative Commons License.

Also goey, revolting, and arguably very unsanitary – but normal.

Here’s a different spin on the same theme, this time in a tortoise beetle larva (Cassidinae):


Photo by Kurt Komoda, on Flickr: Used under a Creative Commons License.

Less slimy, and mobile – but normal. (And still poop).

Fecal shields provide camouflage, prevent desiccation (drying out), and, ironically, can deter predators and parasitoids. Some parasitoids, however, can exploit the fecal sheild and may actually be attracted to the plant volatiles (smelly plant chemicals) in the feces. This could be what happens in the relationship shown in the photo, since the T. julis is a well-established predator of the cereal leaf beetle and, obviously, that goey shield is not much of a deterrent.

So, just to clarify what you’re seeing in the original ZOMGPARASITES photo: in addition to piles of poop, the one visible parasitoid larva is the pale, segmented critter in the front near the beetle larva’s head. Now, its placement is a little odd, because T. julis is normally an endoparasitoid, meaning that the mother wasp lays her egg(s) directly inside the body of the host (the beetle larva). In this case, though, it looks like the parasitoid larva is floating in the fecal shield, so I’m not sure what that’s all about. Lousy aim, perhaps? Even if it was a motherly misfire, I have it on good authority (hat tip to Richard Comont) that the photographer reared out the parasitoid and it did indeed grow up to be T. julis.

So. Long story short:

This is a normal fecal shield, people. Not an imminent explosion.


Chaboo, Caroline (2011). Defensive Behaviors in Leaf Beetles: From the Unusual to the Weird in Chemical Biology of the Tropics, J.M. Vivanco and T. Weir (eds.), 59-69 DOI: 10.1007/978-3-642-19080-3_4

Evans, E., Karren, J., & Israelsen, C. (2006). Interactions Over Time Between Cereal Leaf Beetle (Coleoptera: Chrysomelidae) and Larval Parasitoid Tetrastichus julis (Hymenoptera: Eulophidae) in Utah Journal of Economic Entomology, 99 (6), 1967-1973 DOI: 10.1603/0022-0493-99.6.1967

Schaffner, U., & Müller, C. (2001). Exploitation of the Fecal Shield of the Lily Leaf Beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), by the Specialist Parasitoid Lemophagus pulcher (Hymenoptera: Ichneumonidae) Journal of Insect Behavior, 14 (6), 739-757 DOI: 10.1023/A:1013085316606

24 responses to “Poop, not parasites

  1. Charley Eiseman December 13, 2012 at 11:03 PM

    Thanks for posting this! I spent a little while on Facebook today trying to set people straight. Did you find the original source of the photo? The only thing I found was a comment by Gilles San Martin here suggesting the (correct) ID, and then a follow-up saying he had never seen this in person.

    • TGIQ December 13, 2012 at 11:12 PM

      I tried on Facebook too but when things go viral, single comments get lost in the crowd. The photo on Wikipedia is credited to Gilles, and Richard Comont suggested on Twitter that Gilles had reared it out, so I have every reason to believe it was him?

  2. Colin Favret December 14, 2012 at 6:01 PM

    The image came up in a student presentation yesterday so your posting was quite timely. Thank you! I’ve spread your word:

    • TGIQ December 14, 2012 at 6:15 PM

      Hey, thanks! I appreciate it, and I’m glad that others are helping clear up the misperception (that image has been shared on Facebook thousands of times). Thanks for stopping by and commenting, too!

  3. Dave December 16, 2012 at 9:49 AM

    These larvae carry a cap of wet faeces? Yuck! Sounds like it would be fairly effective at deterring a predator (well, maybe not a dog). Good catch, but good luck in stopping the virus (or should it be viromeme?). If I understand Wikipedia’s criterion for a fact, then if most people believe it to be the fact, it is.

  4. Dave December 16, 2012 at 10:01 AM

    PS – Somewhat off topic, but did you see the Orbeez LadyBug Scooper RC Youtube that BugGirl linked to on G+? Even has a dog.

  5. Adam Blake December 16, 2012 at 12:53 PM

    I saw this on reddit (see url below) on the 13th. The comments there seemed to identify and correct the confusion almost immediately. Was it confirmed that this particular larva was parasitized? A former lab mate of mine works on cereal leaf beetle and I was under the impression that parasitism could only be determined through dissection or rearing. Without knowing the source of the image and the fate of the specimen, I don’t think we can safely say the larvae is parasitized at all.

  6. Katie (Nature ID) December 17, 2012 at 11:06 AM

    Awesome! Thanks for my “learn something new every day” bit. Fecal shield. Ooof, brought to mind all kinds of creative uses and gross imagery. Dalí would have had a field day with this one.

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  8. smccann27 December 20, 2012 at 8:04 AM

    If you do wanna see some heavily parasitized larvae, voila:
    Parasitized caterpillars

  9. biobabbler December 21, 2012 at 1:27 PM

    omg. While I am a biologist, a few things freak me out, and that photo was one. UNTIL YOU told us what was really going on. THANK YOU, jeeze. Rewarded for my bravery (scrolling rapidly as possible past said photo). =) Hooray!!!

    p.s. I’ve had numerous wildlife species defend themselves w/poop, including garter snakes, alligator lizards, etc. Apparently, few species like being pooped on, however the method. =)

  10. biobabbler December 21, 2012 at 1:50 PM

    p.s. who can resist the title of this post?!?

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  13. Joanna June 21, 2013 at 3:33 PM

    Then why is the dome of the “fecal shield” so smooth and regular and contained under what appears to be a membrane of some sort. I will not believe your explanation of the fecal shield until you can satisfactorily answer my question about the smooth, uniform, non-lumpy membrane.

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  17. Vincent Hervet January 17, 2014 at 5:54 PM

    I would like to mention first that I studied the cereal leaf beetle and its parasitoid Tetrastichus julis and I am well aware of their life cycles and identifications. Over the past few years I have made multiple comments on this above picture, but it seems that it shows up on websites faster than I can follow to correct. Here is another comment… I hope it’s useful to some people:
    Yes: this picture shows a larva of the cereal leaf beetle: Oulema melanopus L. Yes: on the back of the beetle larva is its “fecal shield” (mucus filled with its own poop). No: there is no way to tell from this picture if this beetle larva is parasitized by Tetrastichus julis or not (T. julis is an endoparasitoid, which means that it develops inside of its host, not outside, and not in the fecal shield. Only at the parasitoid pre-pupal and pupal stages the presence of parasitoids becomes obvious, as the beetle larva turns into what we call “mummified larva”). Yes: although we cannot tell from this picture, the beetle larva may or not be parasitized by T. julis (the author of this picture mentioned in a previous comment that T. julis individuals emerged from this larva, so it turns out that it was actually parasitized by T. julis, but I insist that there is no way to tell from this picture because the parasitoid did not reach this stage of development yet). No: the “segmented critter” on the side of the beetle larva is not a larva of T. julis. Yes: this segmented critter may very well be the larva of another parasitoid species (or the larva of another insect that somehow got stuck onto the beetle larva’s fecal shield). If it is a parasitoid, then it should be an ectoparasitoid, since occuring outside of the body of the beetle larva. In which case it potentially is a larva of Necremnus leucarthros (Nees), or Pnigalio pectinicornis (L.) (Hymenoptera: Eulophidae). Although neither N. leucarthros nor P. pectinicornis have been reported from North America (where this cereal leaf beetle picture was taken), it possibly is another ectoparasitoid species. It is not uncommon that multiple parasitoid species parasitize the same individual host. In most cases one of the parasitoid species will inhibit the development of the other parasitoid, or predate it. Sometimes they can both develop, and if by chance their larval stage ends roughly at the same time they can both survive to pupate (unless at least one of the parasitoid is a fly, many of these can survive feeding on dead host material).
    For the list of parasitoids of O. melanopus see the online database “TAXAPAD”: For more information on T. julis (and P. pectinicornis) see: “R.J. Dysart, H.L. Maltby, M.H. Brunson, 1973. Larval parasites of Oulema melanopus parasites in Europe and their colonization on the United States. Entomophaga, Vol. 18 (2), p. 133-167”. For more information on N. leucarthros, see: “Jan Gallo, 2007. Parasites on Oulema (Lema) lichenis Voet, 1826. In: Encyclopedia of pest management, Vol. 2. Ed: David Pimentel, CRC Press, p. 447”.

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