As you read this in October, the insect season has probably slowed down a bit. But, as I write this in mid-August (deadlines!) the fireflies are still doing their thing here in southern Wisconsin. It's been a great year for fireflies; they got started earlier in June than normal this year because of our early spring, and they seem to have been more numerous than normal.
Most people are fascinated by how these insects, which are actually members of the beetle family Lampyridae, produce light, but we should also be aware that fireflies and their relatives are beneficial insects, in that they help to control pests. Although the adult stage is very familiar to most people, it's actually the larval stage which is most beneficial. The larvae are active at night, usually on the soil surface or under vegetation, and so are often overlooked by most people. However, many are biolumenescent and therefore called glowworms. The larvae feed on things like snails and slugs, and also soil-dwelling insects such as cutworms.
Here in the United States firefly larvae are primarily terrestrial, and therefore beneficial as predators of crop and garden pests. In some tropical parts of the world there are also species that have aquatic larvae that prey on aquatic snails. These are thought to be important in helping control some human parasites that use snails as an obligate host in part of their life cycle.
So, next summer when you see fireflies flashing once again, remember that they're not just interesting, but also beneficial natural enemies.
- Dan Mahr, University of Wisconsin - Madison
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