Q: I don’t use pesticides, but I have had lawn grub problems in the past. Is there any natural way to get rid of grubs?

A: If you can, plant more flowers, especially with a diversity of species and a range of bloom times. It might sound unrelated to a grub issue, but lots of beneficial insects that prey on garden pests as a natural pest control crew will visit flowers to fuel up on nectar or pollen.

This includes nuisance pests like scarab beetle grubs (Japanese beetle, June beetle, etc.), which have to be more numerous than you might think in order to cause noticeable damage to turfgrass roots. (Visit our Identification of Grubs in Lawns page to learn more about detecting damage and which intervention thresholds should be used for different lawn types.)

One of the best allies in the battle against lawn grubs are wasps, particularly those in the scoliid family. They specialize in hunting scarabs, hovering over lawns to home in on the soil-dwelling grub. Once found, the female wasp digs down, paralyzes it, and then lays an egg on its body. The wasp larva consumes the grub, and violà, you have another generation of grub-suppressing friends. They won’t necessarily eradicate all grubs from a lawn, but they don’t need to – just lowering the population below a damaging threshold is enough.

If you see these wasps zipping about over your grass, just leave them be. They have no interest in people, and won’t be inclined to sting. (Try not to accidentally step on one barefoot, as she’d understandably be a bit defensive.) If you need to mow and a bunch of busy wasps make you wary, wait until early evening when their activity will end for the day. (Trying the morning might work too, but if the grass is dewy, it’s best to avoid mowing turf while it’s wet.)

Males dart around courting females, and the females busy themselves hunting grubs and finding flowers. Favored blooms are those in the mint and aster families, like Joe-Pye weeds and Thoroughworts (Eutrochium and Eupatorium), goldenrods (Solidago and Euthamia), wingstem (Verbesina), and in the photo, culinary mint. Adult flight periods tend to peak in August and September in Maryland.

When feasible, adding blooms to the landscape has multifold benefits, since they can support more insects, which in turn benefit other aspects of the garden and local wildlife. If you can’t squeeze in more flowers, then other options include the use of insect-parasitizing nematodes, which you can find on our White Grub Management on Lawns page.

Q: I was cleaning windows and found what looks like dried grass wedged into the tracks. Do I have a mouse problem?

A: Probably not, as the grass blades were likely stuffed in there by a wasp. Don’t worry – this type of wasp isn’t going to bother people. Appropriately enough, they’re called grass-carrying wasps.

Protected locations like window crevices appeal to them, and the adult wasp hunts other insects (crickets or small grasshoppers in this case) to provision the nest with for her offspring to eat. Like most other solitary wasps, she will not actively care for the new generation; she’ll likely be dead or will have moved on to a new nest by the time the eggs hatch. You can learn more about their life cycle in the Bug of the Week blog entry titled “Window Wasps: Grass-Carrying Wasps, Isodontia Spp.”

These wasps are a curiosity and are not considered pests, so they can be ignored, or their nests removed if they are disconcerting. If window screening that would otherwise block them from accessing a crevice is torn or broken, fixing it is the simplest way to discourage them from using the site again.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.