Horsefly and Deerfly Biology: Life Cycle, Health Impact, and Morphology

Tabanidae: Horseflies and Deerflies

Life Cycle of Tabanus, Chrysops, and Haematopota

The life cycle of horseflies and deerflies (genera Tabanus, Chrysops, and Haematopota) is closely tied to water and is notably long, typically lasting 1-2 years.

• Oviposition: Females lay eggs on plants or stones located close to water bodies.
• Larval Stage: Upon hatching, the larvae enter the water. They are not swimmers but feed on organic matter and plankton. They undergo several larval stages.
• Pupation: The final larval stage burrows into the mud and transforms into a pupa.
• Adult Emergence: Orthorrhaphous adults emerge from the pupa.

Ecology and Ethology

These flies are commonly found in meadows and woodlands near water collections. Ethologically, they are highly active on hot, sunny days, exhibiting diurnal, fast, and silent flight. They primarily locate hosts, such as mammals, by detecting their movement.

Health Importance

Direct Action: Painful Bites

Horsefly and deerfly bites are immediately and intensely painful. They typically result in solitary papules with a hemorrhagic center and subsequent induration. Symptoms include itching, swelling, and redness. The flies' tearing jaws and maxillae create open wounds. They often perform multiple bites on various hosts, which significantly contributes to their role as disease transmitters.

Treatment: Wash the affected area with antiseptics. Apply ointment as needed to alleviate symptoms.

Indirect Action: Vector-borne Diseases

Horseflies and deerflies act as vectors for diseases, notably Loiasis, transmitted by the genus Chrysops.

• Chrysops (Blinding Horsefly): Known for stinging eyelids. These flies typically inhabit wooded areas.
• Haematopota (Storm Horsefly): Often flies in rainy weather and is found in oak and pine forests.

Cyclorrhaphous Diptera: General Fly Characteristics

Cyclorrhaphous Diptera, commonly known as flies, are characterized by their robust bodies, broad wings, and short legs.

Morphology

• Head: Features a pair of large compound eyes, with three ocelli (simple eyes) located dorsally between them. The antennae are situated in a frontal hollow and are composed of three segments; the third segment is often club-shaped and bears an arista (a bristle-like hair). This antennal morphology is crucial for fly classification. Mouthparts vary by genus, being either sucking or hematophagous (piercing-sucking).
• Thorax: Composed of three thoracic segments. The mesothorax (second segment) is the most developed and visible, accommodating the musculature for the single pair of membranous wings. Wing venation, forming distinct cells, is significant for classification. Three pairs of short legs are also inserted here.
• Abdomen: Segmented, typically consisting of 4 or 5 visible segments.

Life Cycle and Adult Emergence

Adult cyclorrhaphous flies emerge from pupae via a process called cyclorrhaphy. This process is facilitated by a specialized organ known as the ptilinum. The ptilinum, located on the front of the head, is a sac-like structure that suddenly inflates with fluid, pushing open a circular suture in the puparium (pupal casing). After emergence, the ptilinum retracts, leaving a characteristic scar on the front of the adult fly's head.

Adult flies generally live for about one month. After mating, females typically lay eggs.