Many people observe flying insects disappearing into holes in the ground. This behavior is a fundamental part of numerous insect species’ life cycles, crucial for their survival and reproduction. Understanding these ground-burrowing flying insects and their motivations provides insight into the natural world.
Common Flying Insects That Burrow
Among the most commonly observed flying insects that burrow are cicada killers, various species of digger bees, and sand wasps. These insects are typically solitary, with each female constructing and provisioning her own nest. While noticeable, they are generally not aggressive unless directly provoked.
Cicada killers (genus Sphecius) are large wasps, 1 to 2 inches long, with black bodies, yellow stripes, and amber wings. Females dig burrows 6 to 10 inches deep and about half an inch wide, preferring dry, sandy, or sparse soil in sunny areas. A distinctive U-shaped soil mound often surrounds the entrance. These wasps hunt and paralyze cicadas, dragging them to their subterranean nests to feed offspring.
Digger bees, including mining bees (e.g., Andrena and Colletes genera), are smaller than cicada killers, often resembling bumble bees with stout, furry, black and yellow bodies. These bees create small, round holes, typically about a quarter-inch in diameter, often surrounded by a volcano-like soil mound. They prefer well-drained, loose, sandy, or clay soils in areas with sparse vegetation. Females line their tunnels with a wax-like secretion to protect eggs and stored pollen and nectar.
Sand wasps (various genera, including Bembix and Sphex) are solitary burrowing insects, often yellow and black or white and black with banded patterns. They excavate nests in loose, deep sand, such as dunes or beaches. Their burrows can be oblique or nearly horizontal, often ending in a terminal cell. Females provision these nests with paralyzed insects, frequently flies, to sustain their developing larvae.
Why These Insects Burrow
Burrowing primarily serves reproductive and developmental needs, ensuring offspring survival. The subterranean environment offers protection from predators, parasites, and adverse weather conditions. Females construct these underground chambers as nurseries for their young.
A primary reason for burrowing is nesting and reproduction; females create safe, secluded spaces to lay their eggs. Burrows function as individual cells where eggs are deposited, often one per cell, allowing larvae to develop undisturbed. Predatory wasps, such as cicada killers and sand wasps, also use burrows for food storage. They paralyze prey (cicadas for cicada killers, flies for sand wasps) and stock these provisions for larvae to consume upon hatching.
Some insects burrow for pupation, a transitional stage where larvae transform into adult insects. After feeding, larvae form a cocoon within the burrow, undergoing metamorphosis before emerging as adults. Burrows can also offer temporary shelter from environmental extremes or predators, though their main purpose remains reproductive.
Identifying Burrowing Flying Insects
Observing specific characteristics and behaviors can help distinguish between different types of burrowing flying insects. The size and coloration of the insect provide initial clues; for instance, cicada killers are notably large with black and yellow markings, while digger bees can vary in size but often have a furry appearance. The presence of distinct antennae or the number of visible wings (two for flies, four for most bees and wasps) can further aid identification.
Flight patterns also offer insights; some wasps might exhibit a direct, rapid flight to and from their burrows, while others might hover. The appearance of the burrow itself is a significant indicator. Cicada killer burrows often have a U-shaped mound of soil at the entrance, whereas digger bee burrows are typically smaller holes with volcano-like soil mounds. Sand wasps often create burrows in loose, sandy areas, and their entrances might be concealed.
Behavior at the burrow entrance can also be revealing. Observing an insect carrying prey, such as a paralyzed cicada, strongly suggests a cicada killer. Digger bees, conversely, carry pollen and nectar into their nests. The presence of multiple individual burrows clustered together, even though the insects are solitary, is common for digger bees and sand wasps, indicating a favorable nesting site.
Impact and Management
Most solitary ground-burrowing flying insects are beneficial to the environment and generally pose minimal threat to humans. Many species, particularly digger bees, are important pollinators, contributing to plant reproduction and ecosystem health. Predatory wasps, like cicada killers and sand wasps, help control populations of other insects, including those that can be considered pests.
While their burrowing activity can create small mounds of soil, potentially impacting the aesthetic of lawns or gardens, this is usually a minor concern. These insects are typically non-aggressive and will only sting if directly provoked or handled roughly. Males of these species are often territorial but lack stingers.
If these insects are in low-traffic areas and not causing significant disruption, the best approach is often to coexist with them. For nuisance situations, non-toxic deterrents can be considered. Improving lawn health, such as ensuring dense grass coverage, can make an area less attractive for burrowing, as many prefer sparse or bare soil. Maintaining soil moisture can also discourage some species, as they prefer dry conditions. Consulting a pest control professional is typically only necessary if there is a large aggregation in a high-risk area or if individuals in the vicinity have severe allergic reactions to stings.