Written by Joe Ballenger

I found a praying mantis egg sac on the small trellis of a potted plant I brought inside for the winter. The plant has started growing on the trellis again, so I can’t remove it. If I put it outside, the plant and likely the eggs, will die. I do have a small hobby greenhouse, but I’m afraid if I put the plant in there, the eggs may hatch and have no food. I’m an avid gardener and would love to have these guys grow up among my vegetables. What should I do? Thanks for your help!

Insects can be…complicated when it comes to enduring winter

Overwintering is actually a pretty complex process. The combination of decreased daylength and lowered temperature tells insects winter is coming. In the wild they can avoid freezing by producing a lot of glycerol and sugar in their blood , which keeps them from freezing solid. Or, they can embrace the cold and allow themselves to become frozen solid by controlling where those ice crystals form, using proteins which control ice formation. To survive the winter, insects either avoid freezing…or allow themselves to become frozen.

Bugs are weird like that.

I think that on some level, everyone knows that insects can survive the winter because they see bugs every summer. Even if you don’t know how they survive the cold, it’s kind of intuitive that they’re able to survive the cold somehow. Otherwise they wouldn’t be there if they couldn’t survive the winter…right?

Accidentally bringing an insect in from the cold happens. When you bring a bug in by accident, it quickly adapts to the room-temperature surroundings and begins developing normally again. They do this because they ‘think’ it’s spring…and if you don’t develop quickly in the spring, you miss the window that’s best for your development.

If you’re a predator (like a mantis), you want to emerge in the spring when everything’s small and easily chompable. This allows you to grow with your prey, and ensures you can eat appropriately-sized things as the year goes on.

While that’s great, from an evolutionary standpoint, it doesn’t exactly help you if you’re a human who accidentally brings in a mantis eggcase from outside and wants to see it survive.

In this case, there’s a few things you can do.

First, you can pop it in the refrigerator to slow it’s development for awhile. It won’t stop completely, but it will last a few months before it dies. As far as I know, there’s no precise measure of how long a mantis egg case will last until it’s no good.

If it hatches, or if you don’t want to keep it next to your butter…there are plenty of mantis-rearing guides on the internet to tide you over until spring. None is better than any other, and they all should cover the same bases.

1.) Mantids are cannibalistic.

Mantids will happily eat their siblings, if given half a chance. They’re voracious predators, and they’re just doing what predators do. If you can keep them individually, do that. If you have to keep them communally because of space constraints, provide lots of cover.

2.) Mantids need small food.

Mantids are small bugs, so they need small insects as food. While it’s snowing, you’re probably not going to find large amounts of insects as food. The way to get small insects is to go to the pet store, and look at what they have in terms of feeder insects.

Typically, in order of size, they’ll have Drosophila melanogaster, Drosophila hyediii, and feeder crickets. D. melanogaster is good for the smallest mantids, and the slightly larger ones will take D. hyedii. After they’ve shed their skin a few times, crickets should suffice until they’re large enough to be separated or released into the wild.

3.) Mantids need humidity.

Cold air tends to lower humidity. Humidity helps insects molt. If you’re raising insects during winter, you need to pay attention to the humidity levels to ensure they can shed their skins.

Mist them about once a day…just to make sure their humidity levels are up to par.

The Bottom Line

Nobody really knows how mantids survive the winter, although they probably use some variant of the two main strategies most insects use. Mantids are not difficult to care for over winter, but you need to be prepared for what’s going to happen if you accidentally bring an eggcase inside. It might not hatch right away, but if it does…you’re going to have hundreds of babies which are trying to eat each other. That’s what mantids do.

However, with proper planning…and with a properly supplied pet store…caring for them until spring shouldn’t be beyond the means of most people. Refrigerate them until you can stock up on fruit flies, and then use the fruit flies to feed them until spring. If they get too big for flies, use crickets.

Be prepared, though, they will  eat each other if you give them a chance. Because of that fact, you will never have 100% survival. In fact, many mantid keepers let them cannibalize to a number they can handle.

It may not be pretty, but that’s the reality you should prepare for if you want to raise mantids during the winter.