Rainy Weather Brings Ants, Flowers and Home-Invading Insects to the Limelight

San Antonio Express News
May 16, 2004

It seems that every weekend since Easter has been loaded with rain, sprinkles, drizzle and any other terms that might be substituted for “liquid sunshine.” These wet conditions have been a blessing for local lawns, pastures, plants, gardens and trees. With these rainy conditions also come increased fire ant activity and the appearance of large cockroaches, pill bugs and small centipedes indoors. What does all of this mean? The apocalypse is near? Not really. This is just a wonderful set of conditions that abound for nature to flourish and do what comes naturally.

As we all know, fire ants and rainfall have an opposite relationship. As rain falls, fire ant mounds rise (from the ground, that is). These rising mounds are doing so in response to elevated soil moisture and the need to provide a moist (not wet) environment in which to produce copious amounts of more fire ants. Sounds like a real positive outlook, right? The good news here is that freshly built fire ant mounds are more vulnerable to treatments right after a rainfall event than at any other time. All of the ants in the mound are within a few inches of the top and are affected more by a treatment at this time. Consider using a hot water drench on these mounds. One gallon of very hot to boiling water on a fresh fire ant mound will produce a 70% success rate on the ants and a 100% success rate on grass kill! Fortunately, the grass will return before the fire ants. Another option at this time is to apply a liquid insecticide to the mounds. Orange oil, insecticide concentrates and other products that can be watered-in will do wonders on a fresh fire ant mound.

Some folks have noticed that winged ants merge from fire ant mounds on sunny days following a rainfall event. These winged ants, or alates, are the “teenagers” of the mound – unmated males and females – seeking to begin new mounds elsewhere. Fortunately, only about 1% of these ants survive to actually begin a mound. The rest are eaten by birds, other insects, and small mammals or just die in some other manner.

Another phenomenon that occurs after rainfall in San Antonio is the home invasions by large cockroaches. The American Cockroach and the Surinam Cockroach are a couple of large outdoor roaches that head indoors during and shortly after it rains. Both of these roaches feed on decaying organic materials in flowerbeds, under trees and near rotting logs and such. While both of these cockroaches are large and cause quite a stir when observed, neither of them prefers to nest indoors. The best options for dealing with them involve baits or some mechanical means of killing them. Combat and Raid have gel-type baits on the market that can be applied in small amounts under the sink or behind places where the roaches would hide. The gel baits are virtually non-toxic to everything but the roaches.

Along the same discussion line, pill bugs and garden centipedes also move in to homes during wet weather. Garden centipedes are brown and reach a length of about one inch long. They feed on organic debris and occasionally find themselves indoors. Once indoors, they usually die because the humidity indoors is too low for survival. These types of centipedes do not bite or sting. Pill bugs essentially do the same thing as garden centipedes. The best ways to control these critters is with a light spray or granular insecticide application around the foundation of the home.

From the bad and the ugly, we finish with the good and lovely. Rains have provided a bountiful crop of wildflowers for the area. Many of the local bluebonnets have gone to seed or will be shortly. This is the perfect time to augment those natural seeds with seed packets for next year’s flowers. For all of the wildflowers currently in bloom, wait until the end of the summer to sow seeds for augmenting next year’s bounty.

This article was written by Nathan Riggs, Extension Agent-IPM, with Texas Cooperative Extension in Bexar County.

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