Robber Fly Life Cycle: A Fascinating Journey Explained

Robber flies, belonging to the family Asilidae, are often considered fascinating and formidable predators in the insect world. As medium-sized to large, bristly or hairy flies, there are over 1,000 species of robber flies found in North America, with nearly 100 species recorded in the Upper Midwest alone Wisconsin Horticulture. These distinctive creatures derive their common name from their aggressive hunting behavior, as they are known for ferociously pouncing from the air on their prey.

The life cycle of a robber fly entails three basic stages: egg, larva, and adult. The specifics of their life cycle may vary depending on the species and their habitat preferences. As a general guideline, those robber flies that hunt on the ground will lay their eggs on or in the soil, while those that hunt from plants deposit eggs into the plant tissues MDC Teacher Portal.

Robber Fly Identification and Characteristics

Physical Features

Robber flies are distinctive and unique insects. Their most prominent features are:

• Large compound eyes
• Three simple eyes (ocelli) on the top of their head
• A dense hair covering their face, called a mystax
• Long, strong legs for grasping prey

Robber flies belong to the order Diptera, which also includes house flies, mosquitoes, and other familiar insects. They are in the suborder Brachycera and are part of the superfamily Asiloidea.

Family Asilidae and Order Diptera

Robber flies are part of the family Asilidae and the order Diptera. Key characteristics include:

• Two wings for flying (typical for Diptera)
• A short, strong proboscis for piercing and sucking prey

These features set them apart from other insects and make them efficient predators.

Subfamilies and Species

Robber flies are a diverse group with over 1,000 species found in North America alone. There are several subfamilies, each with unique features. For example, subfamily Laphriinae is known for its striking color patterns and wasp-like appearance.

Torsten Dikow, a prominent researcher on robber flies, has contributed extensively to the understanding of their classification within the Asilidae family.

Life Cycle and Development

Eggs

Robber flies lay eggs in different environments such as the soil or in plants. Adults deposit their eggs in clusters with each egg being small and cream-colored.

Larvae

After hatching, robber fly larvae are legless, slender, and shiny white in appearance. These larvae are predatory, feeding on eggs, larvae, or other soft-bodied insects, and go through several developmental stages. They usually reside in soil or decaying organic materials, depending on the species.

Pupa

When it is time to pupate, robber flies do so in the soil, where they overwinter. Some species take up to three years to develop from egg to adult, undergoing a series of molts and changes in appearance throughout the process.

Adults

Adult robber flies are characterized by their:

• Two wings
• Prominent spikes on their legs
• Stout hairs on the body
• Sharp, tube-like proboscis
• Large, widely-spaced compound eyes

These features make adult robber flies well-adapted predators, capable of capturing and feeding on various flying insects. Moreover, some robber flies are known to mimic the appearance of bees and wasps to deter potential predators.

Habitat and Distribution

Robber flies are found in various habitats across the globe, from North America to tropical regions, adapting to various environments like desert climates and woodland areas.

North America

In North America, over 1,000 species of robber flies can be found. These predators are often confused with horseflies due to their large size and loud buzzing when flying. They are most active in open habitats, woody edges, and forest glades.

Neotropical Region

Robber flies are diverse and can adapt to various environments, including the Neotropical region. While specific numbers aren’t available for this region, their strong adaptability likely results in a substantial presence.

Desert Climates

• Resilient: Robber flies are known for their adaptability, making them capable of surviving in harsh desert climates.
• Sun-loving: Robber flies prefer sunlit areas, allowing them to thrive in deserts where sunlight is abundant.

Woodland Areas

Robber flies can also be found in woodland areas. These sun-loving predators inhabit forest glades and edges, which provide ample opportunities for prey.

Comparison Table

Predatory Behavior and Prey

Types of Prey

Robber flies are known to prey on a variety of arthropods, including:

• Grasshoppers: A common prey item for robber flies due to their abundance and size.
• Bees: These insects are targeted by robber flies due to their nutritional value.
• Spiders: Although not as common, some robber flies will occasionally capture spiders.
• Dragonflies: A more challenging prey, but still possible for robber flies.
• Ants: Small insects like ants are often captured by robber flies.
• Hymenoptera: This order of insects, which includes bees and wasps, is often targeted by robber flies.
• Beetles: A diverse group of insects, beetles can also fall victim to robber flies.

Hunting Techniques

Robber flies use several strategies when hunting their prey:

1. Aerial attacks: They catch their prey in mid-air, often using their powerful legs to snatch the insect.
2. Ambush: Waiting on a perch until an unsuspecting prey passes by, the robber fly swiftly strikes.

Their predatory habits involve injecting their prey with neurotoxins and proteolytic enzymes, which paralyze and digest the prey, before the robber fly consumes them.

Predatory Impact on Insect Populations

The predatory activities of robber flies can have both positive and negative impacts on insect populations.

Pros:

• Helps control populations of pest insects, such as grasshoppers or beetles.
• Contributes to maintaining a balanced ecosystem by keeping prey populations in check.

Cons:

• Can negatively affect populations of beneficial insects, like bees and other pollinators.
• Possible disruption of food sources for other predatory species like birds, if robber flies consume too many insects.

Mimicry and Defense Mechanisms

Mimics of Other Insects

Robber flies are known for their ability to mimic other insects. For example, some species of the genus Laphria mimic bumblebees by having similar patterns and colorations on their abdomens. They may also imitate other insects like butterflies and moths in order to deter predators.

• Some examples of mimicked insects:
  • Bumblebees
  • Butterflies
  • Moths

Morphological Adaptations

Morphological adaptations in robber flies include features on their abdomen and legs that help them with predation and escaping predators.

• Adaptations in legs:
  • Spines for capturing prey
  • Strong grip for holding onto potential predators
• Adaptations in abdomen:
  • Tapered shape for better agility
  • Sexual dimorphisms in some species for easier identification

Comparison table of morphological adaptations:

In summary, robber flies rely on mimicking other insects and their morphological adaptations to avoid predators and capture prey. Their legs and abdomen play a crucial role in these defense mechanisms.

Reproduction and Mating

Mating Behavior

Robber flies exhibit minimal courtship behavior. Males pounce on females, resembling prey acquisition. Copulation occurs tail-to-tail, with the male and female genitalia connecting together.

Sexual Selection

Environmental conditions play a role in sexual selection for robber flies. Here are some brief characteristics:

• Predators: All species prey on insects
• Wings: Two wings per fly
• Legs: Prominent spikes on legs
• Body: Stout hairs on the body
• Proboscis: Fashioned into a sharp tube or beak
• Eyes: Large, widely-spaced compound eyes

These features enhance their predatory and mating capabilities, making them successful not only in hunting but also in finding a suitable mate.

Conservation and Biodiversity

Impact of Environmental Factors

Robber flies, belonging to the family Asilidae, are opportunistic predators that play a crucial role in maintaining biodiversity. Their population and behavior are affected by various environmental factors such as prey availability and habitat conditions. For instance:

• In areas with higher prey availability, Florida Asilidae populations tend to thrive.
• Habitat loss and fragmentation can negatively impact robber fly populations and their prey base.

Efforts in Conservation and Research

Several efforts focus on preserving and understanding robber fly biodiversity. Here are some examples:

• Research: Ongoing studies aim to better comprehend robber fly biology and their role in maintaining ecosystem balance.
• Habitat conservation: Initiatives that promote habitat preservation help sustain robber fly populations and support biodiversity.

Pros and Cons of Robber Fly Conservation

In summary, the conservation of robber flies is essential for maintaining biodiversity and ensuring ecological balance. Through research and habitat conservation efforts, the preservation of these important predators can be supported.

Resources, Literature, and Identification Tools

Technology and Citizen Science

The identification of robber flies has become easier with the help of technology and citizen science initiatives. One useful resource is BugGuide, a website dedicated to insect identification from the Order Diptera and other orders. By uploading photographs of insects, users can obtain help from experts and other enthusiasts in identifying their finds.

Pros of using BugGuide:

• Access to expert knowledge
• Feedback from a community of enthusiasts

Cons of using BugGuide:

• Might not always provide immediate results

Another helpful tool is the iNaturalist app, which uses AI technology to identify species within seconds, while simultaneously allowing users to contribute to global biodiversity databases.

Pros of iNaturalist app:

• Instant identification using AI technology
• Contribution to global biodiversity data

Cons of iNaturalist app:

• Might not be as accurate as expert identification

Recommended Reading

For those interested in learning more about robber flies and their life cycle, the following resources are recommended:

• Robber Flies | NC State Extension: Provides information on robber flies’ biology and behavior, including their predatory habits and the life cycle of their larvae.
• EENY-281/IN557: Robber Flies, Asilidae (Insecta: Diptera: Asilidae) – EDIS: Offers an in-depth look at the habitats and biology of robber flies, as well as detailed descriptions and illustrations of various species.
• Robber Flies | Missouri Department of Conservation: A comprehensive guide on the identification and habits of robber flies found in Missouri and neighboring states.