Mite morphology

Note: you may find this mite morphology page in the Bee Mite ID tool helpful as well as the training videos on ITP's website.

Overall mite morphology

Normal adult length: <1 mm, range 0.080–20 mm

Body tagmata: capitulum (=gnathosoma), idiosoma

Eyes: +/- 1–2 median ocelli; +/- 1–2 pairs lateral ocelli

Antennae: absent

Mouthparts: 2–3 segmented chelicerae; pedipalps (palps) with 1–5 free segments; pedipalpal coxae fused into subcapitulum

Legs: 1–4 pairs, typically 3 pairs in larvae, 4 pairs in nymphs and adults (rarely 2 pairs, 1 pair)

Distinguishing features: capitulum, loss of visible body segmentation

Overall mite body regions and limbs

dorsal view (left); ventral view (right)

Mites have the first two segments (bearing the chelicerae and palps) separated from the body by flexible cuticle. This anterior region is called the capitulum ('little head') or gnathosoma ('jaw body'). The remainder of the mite body is called the idiosoma and lacks primary segmentation. Larval mites are usually hexapod (6 legs); nymphs and adults usually octopod (8 legs).

Heteromorphic morphology

"Heteromorphic" means having different morphological forms. It can refer either to different forms within a particular life stage (e.g., normal and heteromorphic deutonymphs in some Mesostigmata; protogynes vs. deutogynes in Eriophyoidea; or heteromorphic vs. homeomorphic males in the Astigmata), or to a developmental stage that differs radically from other stages (e.g., the heteromorphic deutonymph or hypopus in the Astigmata).

In addition to heteromorphic deutonymphs and females, which both serve as dispersal or survival stages, some mites, particularly in Astigmata, also exhibit heteromorphic males. These males differ drastically from females, often possessing enlarged legs or chelicerae used for fighting. They typically engage in combat with each other or with homeomorphic males (those morphologically similar to females) but not with females or immatures. Heteromorphic males are produced under low population densities, where they always kill homeomorphic males, eventually allowing the strongest heteromorphic male to monopolize all females in the population. In contrast, heteromorphic males are typically not produced in large populations. A variation of this strategy occurs in the family Pyroglyphidae (Astigmata), where heteromorphic males use their enlarged legs during mating and postcopulatory guarding to prevent other males from mating with the same female.

Mesostigmata morphology—Determining Sex & Stage

Lasioseius male and female

In most cases, identification of Mesostigmata to family or lower can be accomplished only if the specimen is an adult female. The easiest way to determine the stage and sex of your specimen is to look at the intercoxal region. Adult females have a genital opening that is almost invariably in the intercoxal region (species of Metagynella (Fig. 1) are exceptions) and covered by a sclerotized shield which may be truncate posteriorly or continue onto the ventral region. Adult males and immature stages of both sexes have a continuous intercoxal shield that may be truncate or continue onto the ventral region or even incorporate the entire ventral region. Adult males have a subcircular opening in the intercoxal shield (sometimes called a sternogenital or sternitogenital shield) somewhere between the posterior margins of coxae IV (Fig. 2) and the base of the tritosternum (Fig. 3). Immature stages (larva, protonymph, deutonymph) of Mesostigmata have no genital opening.

Fig 1. Postcoxal genital shield

Figure 2; Male intercoxal genital opening.

Fig. 2. Male intercoxal genital opening

Fig. 3. Tritosternum

Female mesostigmatans are easily recognized by their genital opening, usually found between coxa IV and covered by one or more genital shields (Fig. 4). Although called 'genital' (or epigynial, epigynal), the shield protects only the ovipore in mesostigmatans with a secondary sperm transfer system (Dermanyssiae; Fig. 5). Females lay eggs relatively large in comparison to their body size, so the genital opening and its shield are relatively large, and may be extended posteriorly to incorporate ventral or ventrianal elements.

Figure 4; Anatomy of adult female monogynaspid mites, dorsal view (left), ventral view (right).

Fig. 4. Anatomy of adult female monogynaspid mites, dorsal view (left), ventral view (right)

Figure 5; Laelapid-type and phytoseiid-type sperm transfer systems.

Fig. 5. Laelapid-type and phytoseiid-type sperm transfer systems

The genital shield often bears the 5th pair of sternal setae (st5), but may be nude and variously formed. Adult females also usually have one or more shields anterior to the genital shield(s) called sternal shields, and these usually sport one or more of sternal setae st1–4. Other shields cover the ventral and anal regions. The female ologamasid mite in Figures 6 and 7 has a large ventrianal shield, while the female laelapid mite in Figures 8 and 9 has a small anal shield.

Fig. 6. Athiasella female venter

Figure 7; Athiasella female sternal-genital region.

Fig. 7. Athiasella female sternal-genital region

Fig. 8. Stratiolaelaps female venter

Figure 9; Stratiolaelaps female sterno genital region.

Fig. 9. Stratiolaelaps female sternogenital region

Males, however, produce relatively small sperm packets (spermatophores) and have much smaller genital openings. Although these openings also may lie between coxae IV, they are more typically towards the anterior end of the intercoxal region and often at the base of the tritosternum (see details in Figs. 10–13). In the male ologamasid mite (Figs. 10, 11), the genital opening is in a sternogenital (also sternitogenital) shield that bears 5 pairs of setae (st1–5). In the male laelapid mite (Figs. 12, 13), however, the sternogenital shield is fused to the ventrianal shield and other elements to form a ventral shield or plate. Males also often, but not always, have modifications to their chelicerae for transferring sperm, e.g., spermatodactyls or spermatotremes.