Predator or Prey?

Ellipsoptera hamata lacerata | Dixie Co., Florida

Everyone knows that tiger beetles are predators, but look closely at the underside of the head of this female Ellipsoptera hamata lacerata (Gulf Beach Tiger Beetle), photographed in a coastal marsh in Dixie Co., Florida earlier this month.  See the ant head attached by its mandibles to the base of the tiger beetle’s left maxillary palpus?  Detached ant heads latched onto the palp or antenna of a tiger beetle are a fairly common sight—Pearson and Vogler (2001) show the head of an ant attached to the antenna of Eunota togata (Cloaked Tiger Beetle), and Pearson et al. (2006) show one attached to the antennae of Cicindela formosa (Big Sand Tiger Beetle).  I’ve also photographed Cylindera celeripes (Swift Tiger Beetle) with an ant head attached to its antenna.  Pearson and Vogler (2001) and Pearson et al. (2006) both suggest that the ant heads are the result of predation attempts by groups of ants attempting to overpower and kill the tiger beetle, making the ants the predators and the tiger beetles the prey.

Note ant head attached by its mandibles to the base of the tiger beetle's left maxillary palpus.

Although some ants are well known for their predatory horde behavior, I’m not sure I buy this as an explanation for the common occurrence of ant heads attached to tiger beetles.  Tiger beetles themselves often prey on ants, and while I have seen numerous tiger beetles with ant heads attached to them, I have never seen one actually being overpowered by ants (scavenging an already dead tiger beetle, yes—but not overpowering and killing one).  Moreover, the ant heads are nearly always attached to the base of an antenna or palpus—right next to the tiger beetle’s mouth, and almost never on more distal parts of the antennae or other parts of the body.  If the ants were attempting to prey on the tiger beetle, wouldn’t they also (if not even more commonly) be found attached to the tiger beetle’s legs or soft intersegmental membranes?  And how would the ants have come to be decapitated while in the act of attempting to overpower the beetle?  I suggest it is more likely that the ants were prey, latching onto the nearest part of their killer’s body in a last ditch attempt to avoid their inevitable fate.  The antennal and palpal base are about the only tiger beetle body parts that would be within reach of an ant in a tiger beetle’s toothy grasp.  While the rest of the ant was consumed, the head remained because it was firmly attached to the beetle.

I realize that an identification based only on the detached head of an ant may be difficult, but if one is possible it would be appreciated.  The ant head shown in Pearson and Vogler (2001) was identified as Polyergus sp.

REFERENCES:

Pearson, D. L., C. B. Knisley and C. J. Kazilek. 2006. A Field Guide to the Tiger Beetles of the United States and Canada. Oxford University Press, New York, 227 pp.

Pearson, D. L. and A. P. Vogler.  2001. Tiger Beetles: The Evolution, Ecology, and Diversity of the Cicindelids.  Cornell University Press, Ithaca, New York, 333 pp.

Copyright © Ted C. MacRae 2011

About Ted C. MacRae

Ted C. MacRae is a research entomologist by vocation and beetle taxonomist by avocation. Areas of expertise in the latter include worldwide jewel beetles (Buprestidae) and North American longhorned beetles (Cerambycidae). More recent work has focused on North American tiger beetles (Cicindelidae) and their distribution, ecology, and conservation.
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23 Responses to Predator or Prey?

  1. I’d definitely agree with you here, I’m not convinced ants would bother to attack such a strong subject, especially one quite good at flight. I don’t believe it would work unless they had massive numbers and surprised the beetle. I guess it’s not impossible – if ants came across a slightly injured tiger they might try it on but otherwise I think it would be futile.

    Also the fact the beetle is alive and the ant is dead would to me at least preclude referring to this tiger beetle as ‘prey’😉

    • You see ants overpower some very large insects, e.g. katydids and such – but those are often clumsy insects with not nearly the speed and agility of a tiger beetle.

      And yes, it is the beetle that is still alive!

  2. Ben Coulter says:

    Polyergus? Really? I’d be surprised if they could even grasp an antenna with those ice pick mandibles. I would guess Formica sp. would be a more likely candidate identification.

  3. Ben Coulter says:

    Not to flog a dead equine, but Polyergus themselves are specialized slave makers that do not forage for non-host insect prey. Although I suppose if it was being eaten, that could be sufficient motivation! I still say it’s probably Formica.

  4. The prey proposal doesn’t work for me either. It’s like suggesting I was attacked by a flock of turkeys just because I have bits of turkey stuck in my beard after a Christmas dinner.

    I personally think there are some rather vain tiger beetles out there who are collecting trophies of their conquests….;)

  5. Jon Q says:

    No kidding, ants are tough for their size, but the tiger would be the bigger bully in this situation, that ant must of been desperate!

  6. Shoot, I was actually hoping somebody would counter my arguments with convincing reasoning in support of the ant-as-predator hypothesis. Pearson is no slouch when it comes to understanding tiger beetles, so part of me still wonders if I’m just missing something that is obvious to him.

  7. I agree with your explanation, Ted, and with the Polyergus ID (this being a genus I am currently revising, and with which, thus, rather familiar).

    I supect the beetle was drawn to a conspicuous raiding phalanx of the ants. I have seen ground skinks steal the pillaged pupae, and spiders and antlions capture them from returning Polyergus raids. I’ll betchya that’s what happened with this beetle. Though not predacious, since they rely on their host Formica sp. to feed them, these parasitic ants do very effectively use their mandibles defensively, easily piercing calloused human fingers.

    • Interesting that this one also represents a species of Polyergus. Like the tiger in this post, Pearson and Vogler’s tiger (Eunota togata) with a Polyergus head attached also inhabits salt flats along the coast as well as further inland. Time to write a formal rebuttal paper?😛

      • Well, there is a Polyergus that lives in the sandhills at the margins of the salt marshes, that it could be. It’s probably that one, but now you have me doubting a little. Sure wish I could see a clearer, better positioned image of the ant head.

        • I didn’t pay it much attention at the time, but this whole question has me quite intrigued now. I’ll search the collection to see if I per chance have any specimens with ant heads attached and let you have a look. If not, I’ll make sure to collect the next one(s) I see.

  8. Katie says:

    Presumably if the body were still attached to the ant’s head, it would have let go at some point. Your observations of ant heads near the mouth may simply mean the tiger beetle yanked and ate the body. While its obvious who ended up as prey, it provides no evidence of who made the initial predator or defensive attempt. Tiger beetles are not the only ones who carry around ant head trophies. Check out this blogger who caught a diminutive clubtail with an ant head on its front femur: http://nwdragonflier.blogspot.com/2011/03/somebody-lost-her-head.html

    • I suspect the ant whose head is attached to the beetle was not the prey itself, but merely a defender amongst the column of ants the beetle was feeding from. So, in this sense, it really may have been the ant that was the the attacker. Its attack, however, was defensive and not offensive.

      I’ve seen ant heads attached to all manner of things, so I wouldn’t presume that it eventually it would let go if it were not killed or consumed – I can see it just hanging on as a final sacrifice for the colony, dying, and the body breaking away to leave behind only the head.

  9. Jim Johnson says:

    As Katie mentions above, I photographed a dragonfly, Gomphus diminutus, with an ant head clamped onto one of its profemurs (and within reach of its mandibles): http://nwdragonflier.blogspot.com/2011/03/somebody-lost-her-head.html

    I think the explanation of your case sounds pretty reasonable—that the ant was prey and it fought back the only way it knew how. Since dragonflies prey almost strictly on flying insects, that explanation doesn’t work in my case. I figure either the dragonfly landed on the ant when it alighted on the ground and the ant reacted, or the ant made an attack when it came upon the dragonfly sitting on its trail. There’s no way to know for sure, of course. I know virtually nothing about ants, but I imagine that when they come upon potential food (say, a dragonfly sitting motionless on the ground), they have to figure out whether they can start carving it up or not. Maybe a pinch with their mandibles is a way to do that.

    • Cool photo, and as I mentioned to Katie I’ve seen ant heads attached to a number of things. I think there may be a variety of explanations, depending on the situation, but in the case of tiger beetles I still find the predator swarm hypothesis untenable.

  10. Roy says:

    I found this photo showing an individual Ellipsoptera hirtilabris with an ant latched onto the very end of its antenna rather than the base, or on a palpus: http://www.giffbeaton.com/Tiger%20Beetles/Chirtilabris_2005-09-10-0058.jpg

    This would also probably go along with the whole predator swarm hypothesis, as there is no way an ant that size would be able to latch onto the tip of the antenna unless the tiger beetle was already lunging at another prey item.

    • Very interesting. I would agree that the ant latched on for defensive reasons while the tiger beetle was busy preying on the other ants around it.

      James – any idea on the ID of that ant?

  11. James C. Trager says:

    Dorymyrmex bureni (or possibly D flavus, if from west of the Mississippi).

  12. Pingback: Return to Nowhere « Beetles In The Bush

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