Recently, we have been seeing a lot of inquiries on two denizens of dampness; fungus gnats and millipedes. While neither of these arthropods are huge problems, they can become curiosities and annoyances when the weather is as wet as it has been.
Fungus gnats, mostly the species called dark winged fungus gnats, can be occasional root pests. The larval form, which is slimy, slender, and white with a dark head capsule, lives in the soil and feeds on fungi that develop in wet areas. They sometimes will also make meals of plant roots, particularly houseplants and greenhouse plants. As adults, they vaguely resemble mosquitoes and are dark colored and 1/8th inch long.
Currently, the larvae are capturing people’s attention as they perform a migration behavior. Large groups of the maggots will gather together and move en masse as a slimy cohort. This can look like a huge slug or world’s snottiest snake moving through the landscape. When you approach though, they may break apart and try to move independently.
Millipedes are many-legged arthropods that are detritivores; they feed on lots of various kinds of organic matter from fallen leaves to feces. As a group, they tend to have cylindrical bodies and a dark coloration. If you look at them closely, they have two pairs of legs per body segment, one trait that helps to separate them from their cousins the centipedes. They also thrive in conditions that are wet, and so weather such as we have had lately, is quite agreeable to them. Millipedes are occasional invaders of structures but usually perish when entering homes and garages as it is too dry. Right now, Extension clients are sending in photos of millipede marches in their basements and other home areas.
If fungus gnats are outside, there is little that needs to be done for them. They are a natural part of the ecosystem and when things dry out, we will see fewer of them.
If they are inside in your plants, you can use several methods to control the population. Changing the potting medium out, running a fan over the pot to dry out the soil, and water less frequently. You can also treat them with a solution of 9-parts water with 1-part bleach and run it through the soil to kill larval gnats; test this with lesser desired plants first as some may not tolerate the mixture. For an organic approach, use a product containing Bt (Bacillus thuringinesis) specific to flies. One common trade name is “Gnatrol”.
Millipedes will dissipate as well when the weather dries out. If the problem is drastic enough, going through pest proofing procedures to exclude the millipedes should be step number one. Seal up entry points with caulking and check windows and doors for proper seal. You can also place glue board traps near entry points to efficiently capture numerous millipedes for easy disposal. Otherwise, patience and a good broom and dustpan will be your best bets!
By Jonathan L. Larson, Entomology Extension Specialist