Are Anthills Waterproof?

Written by Nancy Miorelli

A few weeks ago I answered a question about what insects do when it rains. Which then prompted this question – what about ants? What about their nests? They are on the ground after all.

Well, are they?

Well, are they?

Well, it’s a little bit complicated (I feel like I have to say this after every question).
With over 12,5oo named species (and probably another 12,000 to go) ants have different behaviors and different types of lodging.

But let’s start out with a general answer.
If you’re thinking about the little ants you find in the sidewalk or in your lawn, they’re generally okay. Rain doesn’t usually penetrate very deep into the soil. Of course that depends on a bunch of factors, like soil type, surrounding plants, how hard it’s raining, how much it’s rained before, and so on, and so forth.

However, ant nests are deep. The shallow ant nests are over a foot into the ground, whereas deep leaf cutter ant mounds can go 26 feet into the ground.

Therefore, rain isn’t a problem. The entrance way might get blocked up but it’s nothing that the ants haven’t dealt with before.

If you live in the south and experience a rainy season (Florida, I’m looking at you), you may find an influx of ants scouting out your home. The constant rain saturates the soil and encourages the ants to find and take up residence somewhere drier. Like your walls.

But let’s have a look at some of the more interesting examples.

Hazards of Beachfront Property

Living in Australia is hard. You’ve probably heard this as practically everything there is venomous. However, when living on beach-front property that floods daily starts looking like a legitimate option – then you know life is really hard.

touches

But that’s what this ant (Polyrhachis sokolova) did. And it’s not just one species. Several species of mangrove ants would rather deal with constant flooding then tackle what the rest of Australia has to offer.

When the tide goes out, the ants flood the surrounding area looking for food debris left by the tide and then swiftly return to their nests. They have to work quickly as they’re racing the clock. Once back inside their nest, the ants move their larva and pupa from chambers of the right temperature to chambers that won’t flood. See, these ants build a special bell-shaped chamber that is pressurized and traps air. There, the ants wait for the tide to recede.

Then the fix their tunnels, reopen entrances, and forage for food again.

Run To The Hills

Some ants want nothing to do with rain or any of that wet stuff. These ants typically make shallow nests that can be affected by the rain. They’ll actually grab their larva and pupa and carry them up to higher ground. Up, out of the nests and onto a tree trunk or a log, or even a rock, where the babies will be safe from the impending doom. Then, when it’s all over, the adult ants will put everyone back safely inside.

On Second Thought – Just Move

Fire ants don’t like the rain. They prefer to nest in dry soil in disturbed areas where they bury underground. They’re kept cool and there’s usually plenty of moisture for them that deep underground.

After a rainstorm, fire ant mounds emerge out of the earth like demonspawn. We’re not sure exactly why the fire ants do this. They may try to access water after dry spells or dry out, or perhaps the soil is just softer to push and manipulate. Either way, fire ant mounds litter the scenery after rain storms.

If there’s too much water and it’s just a lost cause, the fire ants will make a raft and float somewhere else to try again.

I Never Had a Home!

Army ants are always on the move. Rain or shine they’re out scouting the forest for food. There’s no time to stop. It’s unlikely that the rain affects these ants as they typically live in the rain forest. When the ants have eggs, larva, or pupa that they need to take care of, they build a tent out of their bodies that shelter the queen and the young. This is called a bivouac. The bivouac helps the ants thermoregulate during the night when they return every evening.

While I couldn’t find any direct studies about what army ants do when it rains, I’m assuming that if it rains too much, or the temperature drops too low, the ants will return to the bivouac to stay warm. However, because these ants typically live in rain forests, where they have to deal with a rain storm practically every day, it’s unlikely that they would return unless the storm was severe.

An army ant bivouac as seen in the video above. It's just a tent of bodies.

An army ant bivouac as seen in the video above. It’s just a tent of bodies.

TL;DR

We’re talking about some 12,500 species so obviously there are different lifestyles to consider. Some build shallow nests and move their larva and pupa out when it rains. Some just tolerate the wet stuff for a while. Others might seek refuge in your home during the rainy season because no one has time for that. Some ants live in the mangroves, where rain is their least important problem. They clean up the wreckage from tidal flooding every day. Fire ants manage for a while, but if there’s too much rain will float away somewhere else. And some ants, like army ants, just don’t have a home and continue on with their lives rain or shine.

Interested in ant colonies in general? Here’s a cool video by the BBC about the shenanigans that occur inside.

About SciBugs

Entomologist, Science Communicator, and Crafter Twitter: @SciBugs
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One Response to Are Anthills Waterproof?

  1. Pingback: Ants Around Your Trees? 5 Steps to Remove Those Pesky Critters - Hamm's Tree Service

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