Biting Arthropods
of the Lower Suwannee National Wildlife Refuge (LSNWR)

Over the next several months I plan to introduce you to various biting arthropods that you are likely to encounter within the boundaries of the LWNSR. Let me begin by defining what an arthropod is. Arthropoda is the largest phylum in the animal kingdom.  About 84 per cent of all known animal species belong to this phylum.  This phylum includes lobsters, crabs, spiders, mites, insects, centipedes and millipedes.  The distinguishing feature of arthropods is the presence of a jointed skeletal covering.  The body is usually segmented, and segments bear paired jointed appendages, from which the name arthropod (“jointed feet”) is derived. About one million species have been described, of which most are insects. I will be focusing on a sub-group, the biting arthropods, which include mostly insects (mosquitoes, biting midges, yellow flies, horse flies, stable flies, phlebotomine sandflies and blackflies) and acarines (ticks and chiggers).

Culicoides mississippiensis Hoffman

This month’s featured species belongs to the class Insecta, order Diptera (2-winged flies) and family Ceratopogonidae, genus Culicoides.  Collectively, members of this genus are most known as biting midges.  Other common names are no-see-ums, sandflies, biting gnats, punkies and my favorite “flying teeth”.  This is an apt description of the pain the females inflict.

Figure 1A depicts a cartoon drawn by and given to me through a Preventive Medicine officer by a U.S. marine recruit undergoing basic training at Parris Island, South Carolina.  Figure 1B shows a scanning electron micrograph of the actual mouthparts of an adult female.  Figure 1C is a patch worn by some Coast Guard personnel stationed at Yankeetown. There are 47 species of Culicoides known to occur in Florida. The exact number of species occurring within the boundaries of the LSNWR has not yet been determined. Except for mosquitoes, and this may be debatable, no other insects cause more human discomfort to visitors and workers of the LSNWR than several species of biting midges.  Adults are extremely small (ca. 1/8 “long).  They have a distinct wing pattern which is used to distinguish species. Only females take blood, which is usually required to mature a batch of eggs.  Each female will mature 2-4 batches of eggs in her lifetime.  A separate blood meal is required for each batch of eggs.  The life cycle consists of four stages, egg, larva, pupa, and adult. Females lay their eggs on mud. The eggs are very small (0.25 mm); they hatch in 3-5 days.  Larvae go through 4 instars (1/16 -1/8” long), they are creamy white and eel-like in appearance; normally develop in the mud and are predaceous on other small organisms.  Development time is dependent on the temperature and season.  Pupae (1/8” long) also occur in the mud and generally complete development in 3-5 days.  Male adults emerge first, usually 24 hr before the females. Initially, both sexes feed on nectar.  Mating often occurs in swarms.  The males form swarms above shrubs and females enter the swarms and mating occurs.  Usually, after 3-4 days, the females will seek their first blood meal; there are exceptions.

While we haven’t yet identified all the species of biting midges occurring within the LSNWR, there are two species (C. furens and C. mississippiensis) that cause the most discomfort to refuge visitors. Therefore, this month’s featured species is C. mississippiensis. This species breeds in the mud of tidal saltmarshes with vegetation marked by black needle rush (Juncus roemerianus) fringed by Spartina alterniflora cordgrass. Adults are gray and brown with distinct wing markings (Figure 2).

Females are fierce biters and when present cause much annoyance. Females do not bite immediately when alighting but begin ‘crawling about’ in search of vulnerable spots (Figure 3A). The wound produces an intense burning sensation and a small red wheal (Figure 3B), which usually appears in a short time and will persist in most individuals for about 24 hr.

Culicoides mississippiensis occurs throughout the year with very prominent peaks in March-May and October-November.  Upon emergence both sexes feed on nectar from flowering plants.  Ilex vomitoria, which flowers in early spring and is very abundant at several locations (e.g., along the Dennis Creek Trail and at Shell Mound boat ramp) within LSNWR is one of their favorite nectar sources. We have collected large numbers of both sexes from this plant when it is in the flowering stage.  The life cycle of this species differs from most Culicoides species in that the females do not need a blood meal to produce their first batch of eggs.  They have enough nutrients carried over from their larva stage that they can produce the first batch of eggs without a blood meal.  This process is known as autogeny.  All subsequent batches of eggs require a blood meal.  Biting activity occurs throughout the day but is most active in late afternoon/early evening. They are most annoying when there is no breeze.

There is very little that can be done to protect yourself from their biting activity.  Topical repellents work to some degree, but their effectiveness is short lived.  Some individuals like to wear long sleeves and pants with a fine mesh head net.  When using the head net make sure it is secured in a manner which excludes the blood seeking females from getting inside the net or else the face will become an excellent feeding ground!