Many flying insects utilize the ground for various stages of their life cycle, creating burrows for nesting, development, or shelter. While holes in a lawn or garden might cause concern, these insects play important roles in local ecosystems. Understanding which flying insects dig into the earth and why can help people appreciate these creatures and manage their presence. This article explores common types of flying insects that burrow, the reasons behind their subterranean activities, how to identify their presence, and ways to coexist.
Common Ground-Nesting Flying Insects
Several flying insect species are known for their ground-nesting habits, each with distinct characteristics. Mining bees, also known as ground bees, are solitary insects that dig individual burrows, though many females may nest close together in suitable soil conditions. These bees are typically 1/4 to 1/2 inch long and can be dark, furry, or even metallic green. Their activity is usually observed in spring to early summer, lasting only a few weeks.
Digger wasps, a broad category including species like cicada killers and sand wasps, are also solitary and build nests underground. Cicada killers are large wasps, measuring over an inch in length, with black bodies marked by bold yellow stripes and amber wings. Sand wasps, on the other hand, may appear more fly-like with wings that fold across their backs, and they excavate multiple tunnels and chambers.
Cicadas, while adults are known for their loud summer songs, spend most of their lives underground as nymphs. These nymphs can reside beneath the surface for several years, sometimes even 13 or 17 years. Their emergence creates distinctive exit holes. Some species of yellowjackets, unlike many aerial-nesting relatives, also establish communal nests underground. These social wasps often utilize abandoned rodent burrows or other existing cavities, and their nests can house thousands of individuals.
The Purpose of Their Burrows
The primary reason these flying insects create burrows is for nesting and reproduction, providing a protected environment for their offspring. Female mining bees, for instance, dig vertical tunnels with smaller side chambers, where they deposit an egg on a mass of pollen and nectar, sealing it off for the developing larva. This provisioning ensures the young have a food source immediately upon hatching.
For predatory wasps like cicada killers, burrows serve as a secure location to store paralyzed prey that will nourish their larvae. A female cicada killer will sting and paralyze a cicada, then drag it into her underground burrow, laying an egg on the immobilized insect. The wasp larva then feeds on this living, but immobile, food source. Beyond reproduction, these subterranean structures also offer shelter from predators and harsh environmental conditions, such as extreme temperatures or heavy rain.
Cicada nymphs depend on burrows for their life cycle stage, as they grow and molt multiple times underground while feeding on tree root sap. Their specialized digging legs allow them to navigate and create chambers in the soil, sometimes for over a decade, before they emerge to complete their metamorphosis into flying adults. Social ground-nesting yellowjackets rely on underground cavities to build their paper nests, housing their large colonies and protecting the queen and developing young throughout the season.
Recognizing Burrowing Insect Activity
Identifying burrowing insect activity often involves observing specific cues. The burrows themselves offer significant clues. Mining bees typically create small, pencil-sized holes, about 1/4 inch in diameter, often surrounded by a miniature volcano-shaped mound of soil. Digger wasp burrows, particularly those of cicada killers, are larger, approximately 1/2 inch in diameter, with a distinct U-shaped pile of excavated dirt. Cicada emergence holes are generally clean, round openings.
Observing the insects’ behavior provides further identification. Mining bees are often seen flying low to the ground over bare soil where their nests are located. Digger wasps, especially cicada killers, might be seen flying close to the ground, entering or exiting their burrows, or dragging paralyzed prey toward their nests. Yellowjacket nests, which are communal, will have many individuals constantly flying in and out of a single entrance.
The time of year can also help narrow down the culprits. Mining bees are most active in spring, typically for a few weeks, while cicada killers are more prevalent in mid-to-late summer, coinciding with cicada activity. It is also useful to distinguish these from other ground dwellers. Insect burrows are generally smaller than rodent holes, and while some may resemble ant mounds, the hole size and insect activity will differ.
Coexisting with Ground-Nesting Insects
Many ground-nesting flying insects, particularly solitary species like mining bees and most digger wasps, are generally not aggressive. Female mining bees will rarely sting unless directly handled or stepped on, and male bees do not possess stingers. Similarly, cicada killer wasps, despite their large size and intimidating appearance, are not typically aggressive toward humans and will only sting if provoked or trapped.
To safely coexist, maintain a respectful distance and avoid disturbing their burrows. If their presence is undesirable in a specific area, preventative measures can be considered. Ground-nesting bees prefer dry, bare, or sparsely vegetated soil. Maintaining a healthy, dense lawn or covering bare patches with mulch can deter them from nesting. Watering affected areas heavily during their active periods can also make the soil less appealing for nesting.
However, some social species, such as ground-nesting yellowjackets, can be more territorial and aggressive, especially if their nest is disturbed. In situations where aggressive species pose a risk, particularly to individuals with allergies or in high-traffic areas, professional pest control services may be considered for safe removal. Understanding these insects’ behaviors allows for peaceful coexistence, recognizing their ecological contributions as pollinators and pest controllers.