FAQ: Florida Butterflies and Caterpillars in Cold Weather

It’s January, and that means its time for Central Florida to expect a cold snap or two. We get a lot of questions this time of year about how the butterflies and caterpillars handle the cold weather, so we’ve rounded up a few of the most commonly asked and provided the answers below.

How do butterflies handle the occasional cold night in Florida?
Short periods of freezing temperatures (or really any temperature below 55 degrees F or so) cause butterflies to shut down and wait for warmer days. In the Flight Encounter on a cold morning, butterflies can be found hanging dormant from nearly every surface. As the sun emerges and temperatures rise, butterflies begin to warm their bodies in several ways. The most important is sunshine: butterflies will spread their wings and absorb solar radiation. Their efficient bodies can use this energy to raise their body temperature many degrees above the air temperature. When they need a little extra help, butterflies – like humans – can shiver their way up a few extra degrees. Click here to see video of a monarch “shivering” on a cool morning.

Zebra Longwings roosting on a chilly January morning.

Butterflies will remain sluggish and incapable of flight until their body temperatures reach about 80 degrees. If you come across a butterfly basking in the sun on a cold morning, resist the urge to pick it up or move it to a “warmer” location. You can damage the butterfly’s wings and do more harm than good. However, this is a fantastic time to take some good close-up pictures of the butterfly, since it’s unlikely to take off and destroy your shot!

Should I “rescue” the caterpillars in my garden if we’re expecting a frost or freeze?
If the freezing temperatures will only last for a couple of nights or so, there’s no need to worry about the caterpillars in your garden. Caterpillars, like all insects, are pokilotherms, which essentially means that their body temperature is variable. When the temperature drops for a short period of time, insects enter torpor, a state of almost complete inactivity. Their circulatory and respiratory systems slow down dramatically, and they remain that way until the temperature rises again. Many caterpillars will also seek shelter close to the ground, where the temperature is warmer. Click here to learn more about torpor.

Rather than worrying about the caterpillars, you should take action to protect their host plants. Many are cold-sensitive, and if they die back during a freeze, the caterpillars will have nothing to eat when the temperature returns to normal - and then they will die. Take some time to throw an old sheet over your milkweed, passionvine, and other host plants when freezing temperatures are predicted.

Do butterflies in Florida migrate?Yes and no. Most of our monarchs are resident year-round, and do not undertake the massive migration to Mexico many people are familiar with. Other butterflies actually migrate to Florida, like the Common Buckeye (Junonia coenia). And some butterflies undertake short migrations within the state – tropical species like White Peacocks (Anartia jatrophaeis) and Polydamas Swallowtails (Battus polydamas) spend their winters in the more southern parts of the state where freezes are less likely to occur.

If butterflies are in Central Florida year-round, why don’t I see them as often in cooler months?
The answer to that is most likely related to plants and not the butterflies themselves. Like any living creature, butterflies have to move around to find food. Most butterflies drink nectar from plants, and nectar plants can be sensitive to cold temperatures. If the nectar plants in your garden die back or stop producing flowers, you won’t see butterflies in your yard either.

However, almost as soon as you add these plants back to your garden, the butterflies will return. When we suffered the devastating week-long freeze of 2010, all of the nectar plants in my own yard at home were destroyed. The first warm-ish day after, I was at the local nursery, stocking up on cool-weather nectar plants like Tampa Verbain (Glandularia tampensis) and Trailing Bacopa (Sutera cordata). Within less than an hour after planting these in my yard, Gulf Fritillaries were already stopping by to feed.

The host plants in my yard all died, but I still have some caterpillars. How can I help them?
If you can find appropriate host plants at your local nursery, you can buy them and move the caterpillars to them. However, be aware that most nurseries treat plants with pesticides to keep them free of insect damage before selling. You can try washing them well first, but some or all of the caterpillars may still die, as some pesticides are systemic. Since they’ll probably die anyway without host plants in your garden, this option might be worth a try.

If you’re close to a local butterfly garden, give them a call and ask if any of their host plants survived and if they’d be willing to have you bring your caterpillars to their garden. Here at MOSI Outside, we receive several calls each winter from folks wanting to know if we can help their caterpillars. If we have appropriate host plants, we’re happy to have them drop off their caterpillars to be raised in our lab and then released as butterflies in the Flight Encounter. Check our Facebook page for contact info.