Sap Beetles

The scourge of the backyard barbecue and happy hour on the deck are insects commonly called ‘beer bugs’ or sometimes ‘picnic bugs’. These pests seem to love beer and other beverages and happily dive bomb into waiting glasses. Beer bugs are small beetles belonging to a larger group called Sap Beetles. These beetles feed on a wide variety of fruits and vegetables and can cause severe damage to crops when numbers are high.

Beer bugs are about 5-8 mm (¼ inch) long, dark in colour with two noticeable yellow spots on each wing cover. For such a small beetle, it has the improbable name of Glischrochilus quadrisignatus; try throwing that name out at the dinner table. They do not appear to be strong fliers as they often crash land on dinner plates or into wine glasses, but research has shown that the beetles can be attracted for up to 300 meters by odours from food sources. Adult beetles usually start appearing in mid June and peak in numbers between mid-July and early August. Food preferences include raspberries, strawberries, tomatoes and sweet corn. Ripe fruit that has cracks or damage from birds and other insects is often targeted.

Country homes that are surrounded by corn fields often have a bigger problem with beer bugs than houses in town. In the spring, the over-wintering females will deposit eggs in decomposing ears of corn left over from the previous fall. Once the life cycle is completed, newly emerged adults will seek out immature sweet corn. Damaged ears of corn can have 200-400 beetles per ear, one count found 3761 beetles on a single ear of corn.

Since beer bugs are primarily an agricultural pest, control is difficult around the house. The best method is to make up traps that will attract the beetles and place them away from where you will be sitting. Use traps such as those designed for fruit flies or wasps.

Many different types of baits will work, but some that have proven effective include fresh beer, sliced bananas which may be good for up to a week, and 2 day old sliced immature sweet corn (it is not nearly as effective when freshly sliced). Beer has to be replenished daily (whether for the beetles or researchers I’m not sure). Make sure that you place the traps far enough away to avoid attracting the beetles to where you are sitting.

Roll out ... those days of soda and pretzels and beer bugs.