Secrets of the sand trap (Antlions)

Insects for Fun!

This week is a listener request for Antlions! We look into how sand traps are made and what unique tactics antlions use to keep their prey from getting away.

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Transcript:

Welcome to episode 59 of Insects for fun! The entomology podcast hosted by me is your not so local entomologist, and today we have a new listener request from a listener named Joseph out in Hungary! So without further ado let’s dig into it (animal crossing shovel noise)

Antlions are a group of insects in the order Neuroptera which are net winged insects like lacewings and mantidflies and we will definitely be getting to those ones at another time. But today is all about the antlion which are a group of really interesting insects in the family myrmeleontidae of which there are around 2,000! The name antlion appears to have come from the classical era which started in the 8th century before common era, as for why they got this name the most widely believed reason is simply that they prey upon ants like a lion, at least during their larval stage. The insects can be found throughout the world but prefer living in warmer climate areas, especially dry areas like dunes, sandy pine soil barrens like the beach towns in Cape Cod, barren parking lots, basically anywhere that’s got dry or sandy soil. This is not to say they can’t tolerate rain because they can, it’s just that a very rainy area doesn’t exactly pair well with the strategies many of these guys have, and if they are in a rainy place then they choose to make their tunnels underneath cover like fallen debris, trees or or man made structures.

Antlions like all lacewings go through complete metamorphosis, and the larvae are predatory unlike the adults, feeding on ants as well as other small insects, but unlike a lion they don’t chase down their prey. They instead wait for their food to come to them and then take advantage of the moment. Most actually build a funnel-like sand trap and lay in wait at the very bottom. You know the giant sand monster in Star Wars? The one that jabba the hutt would throw prisoners into for fun? I think its name is sarlacc, well that crazy thing is modeled after the larva of an Antlion. OR maybe you’re a star trek fan, in that case think of ceti eel which apparently made its debut in star trek 2 the wrath of khan.

The larvae burrow into the ground butt first and use their arms to fling sand and debri up and out as they form a funnel. Once the trap is made they sit and wait for ants and other insects to walk, slip or fall into their trap. They can tell something is there by feeling the vibrations in the sand using sensory hairs on their bodies which I talked about in a recent episode. These sensory hairs are pretty good and can detect movement of nearby insects that haven’t even entered the funnel trap. Once something has entered the den, the antlion larvae begin flicking sand at the target to create a small landslide, and they are very precise about this, and know exactly how much sand to flick to push their prey to the bottom. If you see videos of these online they absolutely look like sand dune monsters from a sci-fi film. But some species don’t go this far in trap creation, and prefer to stay in premade holes of trees or rocks waiting for something to walk by. Either way these insects are opportunistic feeders, and don’t go chasing down their food. To be honest I don’t think they could even if they tried based on how crazy their bodies are. Of course waiting for your food to come walking by isn’t exactly reliable, and there may be times when little to nothing comes by at all and it's for these reasons that the antlions have very slow metabolisms. They can actually go months without food which actually prolongs their lifespan. That being said, if a location really isn’t providing then the insects will move to a new location. Joseph mentions seeing this happen at the local playground he takes his son to. What’s really interesting and funny is that the larvae move backwards! They could go forward if they wanted, but it’s much easier for them to move this way because of how their body is built. In parts of the US people actually call them doodle bugs because the paths they make in soft soil look like little doodles or drawings made by someone dragging their finger around.

Antlions spend the most time as a larva and only pupate once they’ve reached maximum size. This will of course depend on the species but many antlion larvae max out at around ½ an inch or 1.3cm for our listeners that use the metric system. They stay in this pupa for a month's time before emerging as an adult, but the adults don’t live very long. It’s for these reasons that their lives are extended when little food is present, but the goal of an antlion is not a long life. The adults usually last less than a month with 45 days being very long lived. They do have mouths though! In fact adult antlions are another pollinator, feeding on the nectar from various flowers at night keeping our world green while the butterflies and bees are sleeping. The adults resemble a damselfly, but they have long clubbed antennae and their wings have more of a patchwork pattern which is where the order gets the name, lacewings. You probably wouldn’t encounter one though unless you have lights outside your place at night or you decide to raise one from its larval stage.

But you know who has encountered them? Our friend Joseph who has managed to also raise these in captivity. He actually has a lot of experience with rearing antlions as well as studying them as a fellow insect enthusiast. Fortunately for us he has shared a lot of his knowledge with me to give to all of you listeners! Joseph used to collect antlions by first finding their trails and funnels. He mentioned that it's pretty easy to find them in areas that are covered by shade, like under slides or other structures on playgrounds. To get them out of the sand takes some careful work on the part of us, because simply digging them out with your hands is not only difficult but it could also damage them. Joseph recommends using a filter, or a small thin twig to expose them. I’ve also read online that you can use a straw to gently blow air into the funnel which can show you exactly where they are. Afterwards simply place them in a jar filled with sand. These insects are not picky about what you place them in so long as it's roomy enough. Joseph used 700ml jars, and the cool thing is these larvae will simply go about making a new funnel once moved. They really aren’t bothered by glass walls because they’re not trying to move. As for the food, he told me that these insects will in fact eat anything they possibly can, but bulkier prey items like flies etc are more packed with nutrients and make them grow faster. You can tell the larvae have created a pupae when the sand funnel loses its clean and tidy appearance.

The pupae are buried within their sand pits, and are protected by a cocoon made from silk and sand mixed together. If you have one in a container at this point you will need to make sure it has something to crawl on and enough space to spread its wings. Joseph mentions that the cocoons are almost perfect spheres and are super cool to look at. He actually used a separate container specifically for these, and mentioned that if you raise more than one antlion in a jar it's very important to move the pupa out if the other is still a larva, because the larva will try to eat it…

Now speaking of eating, the mouths of antlions aren’t much of a mouth at all, they’re basically slits that can’t open and close the way we eat food, so the insect must first make their prey edible. To do this the antlions inject a digestive enzyme through their large pincers, and then drink the fluids. Yum. When they finish their food it gets tossed out of the pit, and this can result in a pile of corpses.

Apparently it’s not uncommon for antlions to make dense near each other, and the piles of corpses from one pit might actually help a nearby antlion that hasn’t gotten so lucky because studies show that incoming ants usually don’t fall into traps with corpses and it’s not because they aren’t interested. It’s actually the opposite! Ants will come to investigate but then wander away from the crime scene as opposed to haphazardly walking right into a den. It’s kinda cool to think that in the end the life cycles of antlions could be determined by their neighbors.

Now when it comes to predators, there are different ones depending on the lifestage. Adult antlions will get eaten by birds and bats while the larvae tend to be susceptible to parasitoids, and based on findings from researchers it would appear that 3rd instar antlions are the most at risk for parasitization. It totally makes too because the larger the host is the better. Joseph also mentioned that from wild collected antlions the rate of parasitization was pretty high, basically it comes down to how young the antlion larva is when you find it. The younger the better if you want the best chance of avoiding an unwanted wasp.

Thanks for listening to this episode of Insects for Fun! As always if you’re enjoying the podcast it is incredibly helpful to rate it and leave a review! If you would like to further support the show, get bonus episodes and other side content be sure to check out the show on patreon.com/insects for fun.

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