Where do the invertebrates in the garden go over winter?
Our Pennsylvania gardens are home to a variety of invertebrates such as insects, spiders, centipedes, snails, and many others. We see these creatures throughout the spring, summer and fall months. But what happens to them in the winter?
Do they die? Do they leave? Do they hide? Do they hibernate? The answer is yes to all of these questions! Invertebrates have evolved multiple, often fascinating strategies to survive.
Generally, invertebrates go through a life cycle starting with eggs that develop into larvae or nymphs, sometimes pupae, then adults, with variation among the different groups of organisms. Overwintering can occur in any of these stages depending on the group of invertebrates.
Organisms that rely on their eggs surviving winter include the praying mantises, who will deposit their egg case on a branch or stem where it will protect the eggs until spring. Blackflies deposit their eggs into the running water of a stream where they get lodged into a crevice in the stream bottom until spring when the larvae hatch and begin to feed underwater.
The invasive spotted lantern fly deposits large egg masses on various outdoor surfaces. In the fall months, grasshoppers bury their eggs deep in the ground.
Many organisms overwinter as larvae. These organisms include beetle grubs, who usually burrow down into the soil, and many caterpillars of butterflies and moths that nestle into the leaf litter.
Some species of flies deposit their eggs inside the green stem of a plant which causes the plant to form a gall around the egg. The larvae hatch within the gall and survive the winter protected by the gall.
Pupae are the life stage where the larvae encapsulate themselves and metamorphosize into an adult. This stage does not move or feed and therefore is a suitable form for overwintering. Many butterflies and moths form a silken chrysalis and overwinter as pupae.
As for those invertebrates that overwinter as adults, most will try to find a sheltered place to hide such as tree holes, cervices under bark, loose leaf litter on the ground, cracks under the eaves of a house or often inside a house if they can find their way indoors. Ladybird beetles, mosquitoes, pill bugs, snails, centipedes and stink bugs often aggregate in large numbers in such places.
In any of these overwintering life stages, the invertebrates often enter a dormant state called diapause, where some of the water in the organism is replaced by a chemical that acts as an antifreeze so that cells are not destroyed by freezing. Metabolism slows and they neither move nor eat. All of these strategies for overwintering have one commonality: They all are a means to pausing the life cycle until the warm weather arrives. The organisms do not feed, grow, or mate.
Some groups of invertebrates do remain active all winter by seeking out warmer climates. Monarch butterflies fly three thousand miles for the warm climates of California and Mexico until they fly back in the spring. But there are also some groups that have found microclimates closer to home that maintain temperatures warm enough to allow activity all winter.
Because water under frozen lakes, ponds, and streams usually stays at 4 degrees Celsius, dragonflies, mayflies, and stoneflies are able remain active overwinter as aquatic nymphs (a type of larvae that often resemble the adult stage but without wings). They feed all winter and, in the spring, emerge from the water and finish their metamorphosis into adults. Honeybees modify the climate in the hive by vibrating their wings to produce heat. They rely on their stores of honey to fuel this activity.
Lastly, there is a microclimate that many do not realize is right under their feet. A layer of snow on the ground acts as a blanket and insulates the area beneath it from the colder air temperatures; the temperature under the snow does not go below 0 degrees Celsius.
A layer of leaf litter can maintain an active population of numerous invertebrates throughout the winter. Some groups of springtails and spiders, and a group of wingless insects called Chionea, or snow flies, will even find their way up to the snow’s surface on a sunny day.
Our garden habitat should be hospitable for invertebrates throughout the year. Leave leaf litter and dead stalks of perennials to support the winter survival of invertebrates.
Wait until spring is well on its way and the invertebrates have come back to life to clean up your garden.
If you have questions about natural gardening practices or support invertebrate populations, call the Butler County Master Gardener Garden Hotline at 724-287 4761, ext. 7, or email the Master Gardeners at butlermg@psu.edu.
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Carol Chmielewski, MSc, is a Penn State Extension Butler County Master Gardener.
