11
$\begingroup$

There aren't any eusocial animals (hives of wasps, ants, termites, etc) that hunt large prey, are there?

I'm thinking prey in the size range of, say, a rabbit, or even a deer.

I can't see a rabbit or a deer having any real effective way to defend against a swarm of hornets, especially if you supposed that the hornets' venom could easily be adapted to be particularly effective against such prey.

Intuitively, this seems like it would be a lucrative little niche.

Like:

  • A swarm could bring down a kill without risking losing too many members.

  • The return seems like it could be very high.

  • There shouldn't be too much of a risk of losing much of the kill to scavengers or whatever.

  • And after starting down the evolutionary pathway into such a niche, they could easily develop methods of preserving meat (I'm imagining a horrifying hive full of natural ham, here).

  • Protecting this ham-hive wouldn't be any more difficult than protecting a honey-hive from bears etc.

And such a niche doesn't seem that evolutionarily distant from where hornets already are.

Like:

  • They already do seriously hurt or even kill large animals that they perceive as threatening their hive.

  • They already do scavenge large animals they find dead, and even steal the occasional chunk of flesh from living animals.

But as far as I know, nothing like this exists, right?

Why not?

(And, like... maybe the most important question: How can we make sure it never comes into existence?)

$\endgroup$
  • 4
    $\begingroup$ Army ants regularly kill and eat birds (although they primarily hunt insects). Dorylus, or siafu ants consume rats and are considered a menace to humans with restricted mobility. And [invasive] bees do kill humans although we are not prey. $\endgroup$ – Luigi Jul 24 '15 at 14:35
  • 3
    $\begingroup$ @Luigi Yeah, that kind of stuff is essentially what I meant about them already being pretty close to that niche. That is, those are examples of eusocial insects with behaviors on the edge of the "ham-hornet"-like niche. My question is, why haven't any species fallen right smack-dab into the middle of it? Ya know what I mean? $\endgroup$ – Owen_R Jul 24 '15 at 15:14
  • 3
    $\begingroup$ I wonder whether hornets &c can effectively sting through fur? Then there's the sheer number of stings that it would take to kill a non-allergic animal. $\endgroup$ – jamesqf Jul 24 '15 at 17:44
  • 1
    $\begingroup$ @jamesqf In case you think sting victims who die only die of allergy reaction (anaphylactic shock), some species of hornets actually have a sting that contains neurotoxins, and some can cause kidney failure. E.g.: the Asian giant hornet $\endgroup$ – Kal Jul 25 '15 at 1:07
10
$\begingroup$

They're not fast enough

A hornet has a top speed of around 40 kph, while a rabbit is only a touch faster, a deer can hit 75 kph (all figures from Wikipedia). In order to act as hunting insects they need to match the speed of these large animals in large enough numbers to surround and overpower them but these animals could easily match their speed or outpace them. Let's suppose they can overcome that limitation somehow and bring the prey down. They've now bagged a big lump of protein but it's a long way from the hive because they've had to chase it down first. That means that a long round trip is required every time they visit the kill and thus reduces the energy yield as well as increasing the chance of losing it to scavengers.

Against this you have the simpler option of eating smaller, easier to catch, prey as they do now.

$\endgroup$
  • $\begingroup$ Alright, that's the first idea that feels like a potentially satisfying answer, thanks! :D So in order to wander into this niche, they'd need to at least start by hunting animals that can't accelerate away as quickly, but those seem like they'd be less common (so it'd be less lucrative) and/or much more massive (so they'd need to also happen to have stronger venom). Of course, it might also work if the hornets were able to sneak up and surprise animals, but those kind of stalking behaviors are complex and not very close to their current behaviors... $\endgroup$ – Owen_R Jul 24 '15 at 16:06
  • $\begingroup$ Alright, yeah, I'm starting to feel like I'm getting a sense of the kind of barriers that prevent a species from simply wandering into this "ham-hornet" niche. Thanks again! :D Think I should mark this as accepted? Do you have any other ideas to add? $\endgroup$ – Owen_R Jul 24 '15 at 16:08
  • 2
    $\begingroup$ Moreover they have to masticate the prey to feed the larvae. It would not be feasible with big animals. $\endgroup$ – WYSIWYG Jul 24 '15 at 17:53
  • 1
    $\begingroup$ @Owen_R: The comparison between honey bees and hornets is moot; the comparison which is evolutionarily relevant is to investing their energy in hunting small prey as they do now. In order to start hunting large prey they need to get a benefit from ineffectually hunting these prey since they have not yet adapted to do it well. $\endgroup$ – Jack Aidley Jul 24 '15 at 21:38
  • 2
    $\begingroup$ I'd argue that it's not so much they aren't fast enough movers, more that they are not fast enough killers. The note below about the army ants killing a worm... that's a worm, not known for its ability to sprint, and it got 3m or about 10ft. They then butchered it in situ, rather than carrying it back in one piece. For a flying hunter, you have better range, but still... I suspect that most large animals, being attacked by killer bees, will run away far further than is feasible to recover their flesh, and will also do what they can to harm the bees, rolling etc. Sounds maladaptive. $\endgroup$ – Dewi Morgan Jul 25 '15 at 21:02
8
$\begingroup$

They do exist. Many such examples can be found. Such as the most terrifying one, being social groups formed by Spiders, Anelosimus eximius documented here.

Colonies of upto 9000 individuals have been documented by the scientists in their report.

Also let's not forget Piranhas, another group of social animals, which take down much larger prey due to their larger colony size.

This particular phenomenon is concisely explained in this article in wikipedia under Cooperative Hunting

As the models explain and I also think the same, that the only reason a social aggregation would seem necessary to any animal is because it provides increased fitness or survival. This particular phenomenon can be viewed from the perspective of Human society as well. I given an income source X, would always choose to rent a private space for myself. If my income does not allow me such an option my best option is to cooperate with another in a shared system.

So the same can be said for Insects if availability of prey which can be candidates of solo hunting goes down, the only option left for the species to survive is to either compete if that is the only available source of food, or if larger prey is available for group hunting where individuals don't come into direct conflict, then to go for the option which provides the greatest fitness to the species as a whole. Obviously, in such a case you go for aggregation and not competition such as those seen in ant colonies.

Many more such systems exist I am sure, but I am no evolutionary biologist only a humble genomics guy. They will be able to provide much more comprehensive answers.

$\endgroup$
  • 1
    $\begingroup$ Well, that's interesting, but it seems like kinda a non-sequitur to my question. Eusocial insects seem like they'd be really effective in a niche focused around cooperative hunting, especially if they bring down prey hundreds or thousands of times more massive than an individual member of the swarm, and then store the meat in their hive. But apparently they don't do that. My question is, why not? These spiders aren't eusocial, and they're not cooperating to catch prey that much more massive than the individual spider. $\endgroup$ – Owen_R Jul 24 '15 at 15:32
  • 1
    $\begingroup$ I would disagree on the point of eusociality as this study states rd.springer.com/article/10.1007%2FBF00300005. Can they bring down something which is a hundred or thousands to times larger than them? No I do not think so, but as the investigative group notes in the answer, they do not really catch the same number of prey. Rather, they catch a much smaller number of prey of increased biomass culminating ultimately towards more biomass per spider than they would have gotten individually. $\endgroup$ – FoldedChromatin Jul 24 '15 at 15:47
  • 2
    $\begingroup$ Hm, yeah, everyone knows that the stereotypical individual spider "wraps up flies for later", even. But still, do you really think this is actually a direct answer to my question? Or just interesting, potentially related information? It makes sense to me as the latter, but not the former. $\endgroup$ – Owen_R Jul 24 '15 at 17:28
  • 1
    $\begingroup$ While piranhas can take down very large prey, such as cattle, that is not their ordinary behavior by far, and actually quite unusual. Attacks on large animals and humans are typically non-fatal, with some nips and bites taken, but the victim usually can escape. Fatal attacks occur with children, impaired or disabled adults (such as drunkenness), and at the peak of the dry season when water levels are very low and food is scarce. Studies have actually shown that they are rather timid fish, using their teeth primarily for defense. $\endgroup$ – MattDMo Jul 25 '15 at 3:32
  • 2
    $\begingroup$ Your giant spider colony example completely misses the point. Yes, they exist in large colonies, and larger webs can catch somewhat larger prey "several times their body size" (from your link), but they do not hunt much larger species like the OP is looking for. I don't think s/he doubts cooperative hunting exists, they're just looking for examples of individual predators being orders of magnitude smaller than their intended prey. $\endgroup$ – MattDMo Jul 25 '15 at 3:38
3
$\begingroup$

Unfortunately for you, such animals do exist (O'Donnell et al. 2005).

This is a direct field observation of a swarm of army ants attacking and consuming a 60cm long earthworm, as well as consuming a 10cm long snake.

From the linked article:

We collected workers from two Cheliomyrmex andicola foraging raids. During raid 1 on 26 September 2003 at 1030 h, we encountered a large C. andicola raid column in primary terra firme forest, exiting from soil-covered foraging trails that the ants had constructed on a slope. The sky was clear, and ground surface temperature was 25.9°C. Beneath the raised tunnel of soil particles that the ants had constructed, we found the partially consumed carcass of a snake (1 cm in diameter and 10 cm long). Most of the snake's scales and skin had been removed. Cheliomyrmex andicola workers were observed chewing on the snake and carrying away bits of flesh in their mandibles. As we dug near the carcass, the ant workers responded by biting and stinging our hands. The workers clung to our skin, and we noted that their stings were more painful than those of other army ants from the site (e.g., Eciton burchellii and Eciton hamatum). We collected ant workers and samples of snake flesh into 70 percent ethanol. During raid 2 on 1 October 2003 at 1205 h, during a brief rain shower, our attention was drawn by rustling sounds in the leaf litter on a slope in a partially cleared area of terra firme forest adjacent to the station buildings. A subterranean column of C. andicola workers erupted from the soil in pursuit of a fleeing giant earthworm (possibly a species in the genus Martiodrilus: Zicsi 1990). Several hundred ant workers emerged from the soil and ran over the leaf litter in the direction taken by the worm. Five C. andicola workers mounted the worm and were biting and apparently stinging its body. After the worm crawled for a distance of 3 m down slope from where it exited the soil, its body contracted from over 40 cm in length to approximately 20 cm in length. The worm abruptly stopped moving and became rigid on the soil surface within 10 sec of exiting the soil, and was then unresponsive to human touch. We assumed that the worm was either paralyzed or dead. We lifted the worm to examine it, and we collected ant workers from its body and from the raid column as it arrived where the worm came to rest. Workers collected from both raids had no prey (other than snake flesh at raid 1) in their mandibles.

However, most army ants are (fortunately) not predators of large animals. This appeared to be the only unambiguous literature reference of predation of large animals by eusocial insects that I could find in a brief literature search.

$\endgroup$
  • $\begingroup$ Sigh. Okay yeah, that sounds like what I was expecting. No hornet ham-hives, though? I guess the obvious follow-up question is: How can we kill them all? I guess we should really just migrate into space and then nuke the entire horrible planet to be sure.... Do we have enough nukes? Do we need more nukes? Maybe we could just fling it into the sun, to be sure... $\endgroup$ – Owen_R Jul 24 '15 at 14:53
  • $\begingroup$ @Owen_R Actually, despite the fact that they can prey on animals much larger than themselves, many army ants are themselves preyed upon. For example, driver ants are often eaten by chimpanzees $\endgroup$ – March Ho Jul 24 '15 at 14:57
  • 1
    $\begingroup$ That joking aside, though, I still feel like it should be surprising that this isn't a more prevalent strategy. The lack of ham-hornets seems like it needs an explanation, ya know? $\endgroup$ – Owen_R Jul 24 '15 at 15:07
  • $\begingroup$ Also, I find myself focusing in more and more now on this idea of "ham-hornets", and I think there are actually good theoretical reasons to focus on it. Flying hornets would be particularly effective at attacking a rabbit~deer, since they can attack from all directions and are so individually manoeuvrable. That is, it's a lot easier to imagine escaping from a swarm of ants crawling up your leg than a swarm of hornets flying all around you. So it seems like it should be additionally surprising that we have reports of ants acting like that but not hornets. What might be preventing ham-hornets? $\endgroup$ – Owen_R Jul 24 '15 at 15:45
  • 2
    $\begingroup$ Army ants have been reported to kill and butcher animals that were unable to get away - babies in cradles, tied up goats, etc. Speed of killing really does seem to be the issue here. Japanese tiger hornets are huge, have a potent venom, and inject a lot of it, which kills dozens of humans every year... eventually. But because it's slow-acting, they don't use their sting for hunting, just for defense. For hunting, they use their mandibles, and bite the heads off stuff. Some hunter wasps can paralyze smaller prey, which would give more time for killing, but they can't paralyze anything big. $\endgroup$ – Dewi Morgan Jul 25 '15 at 21:35

protected by Chris Jul 24 '15 at 21:08

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.