Wednesday, November 20, 2013

Uninvited Holiday Guests

Insects, like all animals, must survive the winter (in one way or another) to reproduce the next year. There are two main strategies to do so: migrate or "hibernate". Of course there are famous insect migrations including monarch butterflies (Danaus plexippus) and several species of dragonflies (Odonata). However it is much more common for insects (and other arthropods) to hunker down for the winter in a nice secluded place. Insects overwinter in different life stages - either as eggs, larvae/nymphs, pupae (if they are holometabolous), or adults. The stage that overwinters usually depends on the type of insect, but sometimes can be determined by environmental or geographical factors.

Thus, as the days begin to cool and darkness descends earlier in the evening this holiday season, you may be getting more than your in-laws invading your home. Most do so by finding a nice brightly-colored home as a landmark during warm days where they aggregate on the siding, in eaves, or along windows. The most common nuisance insects overwinter as adults that may become active within homes during warm days of the season - a common occurrence here in NC which has a mild, fluctuating winter. Mass movements of these insects into living areas can be difficult to deal with and are a real annoyance. The following are some of the more common insects to enter houses.

- True bugs (Hemiptera) - the worst offenders -

Kudzu bugs aggregating in the crack of a tree; could easily be a window or the gaps in the siding of a house.

Bugs are among the most common insects found aggregating on and entering homes in the cooler months. Their numbers and the pungent smell they produce (they're not called stink bugs for nothing!) can be bothersome to people that want to enjoy the comforts of their indoors. Although bugs are generally harmless, kudzu bugs (Plataspidae: Megacopta cribraria) are sometimes known to cause irritations on skin, brought about by the secretions they produce. Brown marmorated stink bugs (Pentatomidae: Halyomorpha halys), another recent introduction into the US, also find it nice and cozy in houses. Along with these invasive bugs, many other types, including leaf-footed bugs (Coreidae: Leptoglossus) and boxelder bugs (Rhopalidae: Boisea trivittata), enjoy breaking and entering for a nice place to hibernate.

Kudzu bugs: one is alright, but hundreds are bad news!
Brown marmorated stink bugs find your home when it's cold outside.
Leaf-footed bugs may be seen around the home.

- Flies (Diptera) - can we use your attic? -

Figure from Oldroyd's magnificent book, The Natural History of Flies (1964). 

Several groups of flies will spend the winter in attics, barns and other man-made structures, safe and cozy away from the elements. The most common are called cluster flies (Calliphoirdae: Pollenia sp.), named for the fact that they often "cluster" in groups of hundreds in the attics of homes. Normally they are out parasitizing earthworms, but in the fall and winter when things slow down they get the urge to swarm homes. Face flies (Muscidae: Musca autumnalis) will also do this, usually around areas with livestock, their primary food (larvae live in dung and adults feed on facial secretions). On warm days these flies may come out of hiding to stretch their wings, much to the dismay of homeowners.
Cluster flies are drab (for blow flies) and have golden hairs on their thorax.

- Ladybugs (Coccinellidae) are pretty - but get them out of my house! -

"Ladybugs are great, right? They eat all the pests and are nice to look at." Tell that to someone whose living room is overrun by these red and black beasts. Most ladybugs do a fine job of staying outside and being good neighbors. However, one species in particular (though there are a few others) - the multicolored Asian ladybug or harlequin ladybug (Coccinellidae: Harmonia axyridis) - loves to come into homes. This highly variable species was first introduced into the US in 1916 for the control of pests and has been readily available for farmers and homeowners to purchase. In the 1980s it finally became established, and is now the dominant ladybug in much of its range. Thus there have been some concerns about this species. First, it may be pushing out native ladybugs with its voraciousness, which is not good for our biodiversity. Second, it can be structural nuisance pests. Along these lines, when they do enter homes in large numbers they can sometimes bite people and, like many ladybugs, reflexively bleed a noxious substance that may cause skin irritation and allergic reactions. For both of these reasons, the cartoon-like insects can be less funny than they are nightmare inducing.

Multicolored Asian ladybugs, though sometimes beneficial, are often a nuisance.

- So what can you do about it? -

The best way to deal with these insects is to first make sure that they cannot enter your home. Search for cracks and holes in the siding or under eaves. Any crack or hole small enough for the average insect to enter should be repaired or covered. While pesticide sprays on the South sides of the home may kill or deter some insects, they are not long-lasting, nor are they particularly effective. Once in the home, it is best to vacuum the insects up and collect them into hot soapy water or freeze to kill them. Spraying indoors usually does more harm than good, so cultural practices mentioned above work best.