Identification and Characteristics of Major Silkworm Pests

Sericulture – the practice of rearing silkworms for silk production – is an ancient industry that supports the livelihoods of millions of farmers across Asia. Yet despite careful rearing practices, silkworm crops face persistent threats from insect pests that can wipe out significant portions of a harvest if left undetected. Two of the most damaging culprits are the Uzi fly (Exorista bombycis) and the Dermestes beetle (Dermestes spp.). Knowing how to identify these pests accurately is the first and most critical step in protecting any silkworm rearing operation.

Why pest identification matters in sericulture 🔗

Pest identification is the foundation of effective crop protection. Without knowing exactly which pest is present, farmers risk applying the wrong control measures – wasting resources and potentially making the problem worse. In silkworm rearing, the stakes are particularly high because both major pests strike at different life stages and locations: one attacks living larvae inside the rearing house, while the other targets stored cocoons and grainage rooms. Recognizing their physical characteristics and the signs they leave behind allows sericulturists to intervene quickly and precisely.

According to research published by Springer on silkworm diseases and pests, crop losses in India due to insect pests and diseases range from 15 to 47%, with pests like the Uzi fly and Dermestes beetles contributing substantially to these figures. Understanding what these pests look like is non-negotiable for any serious sericulturist.

The Uzi fly (Exorista bombycis) 🔗

The Uzi fly is widely regarded as one of the most destructive insect pests in silkworm production. It belongs to the family Tachinidae – a group of parasitic flies known for targeting other insects as hosts for their larvae. A review published in Integrated Pest Management Reviews identifies at least four species of Uzi fly that attack silkworms, with Exorista bombycis being the primary species affecting the mulberry silkworm (Bombyx mori) in India and across South and Southeast Asia.

Physical characteristics of the adult Uzi fly 🔗

At first glance, the Uzi fly can be mistaken for a common housefly, but several features set it apart on closer inspection. The adult is noticeably larger than a housefly, with a body length of approximately 8-12 mm. Its overall coloration is blackish-grey, giving it a dull, muted appearance typical of many tachinid flies.

The most diagnostic feature is the presence of distinct black longitudinal stripes on the thorax and abdomen. These stripes run along the length of the body and become clearly visible under good lighting. The thorax is well-developed and robust, consistent with the fly’s strong flying capability. As noted by Britannica’s entry on tachinid flies, most tachinids are bristly and more robust than houseflies – and the Uzi fly is no exception. Its body is covered with stiff bristles, particularly on the abdomen, which is another feature that distinguishes it from the smooth-bodied common housefly.

The wings are clear and fully developed, enabling the fly to enter rearing houses and locate hosts efficiently. The compound eyes are relatively large, and the antennae are three-segmented with a prominent postscutellum – a raised flap visible beneath the scutellum – which is a hallmark of the Tachinidae family.

Larval and egg characteristics 🔗

The eggs of the Uzi fly are small, white, and ovoid, and are deposited directly onto the body surface of silkworm larvae – typically one or two eggs per larva. The preferred laying sites are the dorsal and dorsolateral surfaces of the silkworm’s body, particularly in the intersegmental regions. According to the Central Silk Board of India, once laid, the eggs hatch within 2-3 days and the emerging maggots burrow inside the silkworm’s body, where they feed on internal tissues for 5-7 days before rupturing the host and emerging to pupate.

Signs of Uzi fly infestation 🔗

The visible signs on an infested silkworm include black scars or egg deposits on the larval body surface – these are the glued-down eggs that cannot be easily removed. In cocoons, the tell-tale sign is a circular maggot emergence hole at the tip of the cocoon, left behind when the mature maggot burrows out. Infested larvae become sluggish, lose their appetite, and fail to spin properly. The Central Silk Board reports that E. bombycis inflicts 10-15% damage to cocoon crops in major silk-producing states such as Karnataka, Andhra Pradesh, and Tamil Nadu, with severity peaking during the rainy season.

The Dermestes beetle (Dermestes spp.) 🔗

While the Uzi fly attacks living larvae, the Dermestes beetle poses a distinct threat at the storage and grainage stage. These beetles belong to the family Dermestidae (order Coleoptera) and are commonly known as hide beetles or skin beetles. Several species are associated with the silk industry, with Dermestes ater (the black larder beetle) being the most commonly reported pest in sericulture settings in India.

Physical characteristics of the adult beetle 🔗

Adult Dermestes beetles are elongate and oval in shape, with a body length of approximately 7-9 mm. The overall body color is black to dark brown. According to Wikipedia’s entry on Dermestes ater, the adult has black or brown wing covers (elytra) with a coating of fine yellowish hairs scattered across the body. Males can be distinguished from females by a row of bristles along the abdomen.

The elytra cover most of the abdomen and give the beetle its characteristic smooth, hardened upper surface. The antennae are clubbed – a feature typical of the Dermestidae family – and are usually tucked into a groove on the underside of the thorax when the beetle is at rest, making them less visible. The Dermestidae family profile on Wikipedia notes that adults of Dermestes species are found in association with animal carcasses and stored products, and their connection to silk production is well-documented across India and other sericulture regions.

Larval characteristics 🔗

The larval stage is where Dermestes beetles cause the most serious damage in silkworm operations. The larvae are elongate, covered in dense, long bristles (setae), which is one of their most distinctive identification features. These bristles are dark – reddish-brown to black – and give the larva a distinctly hairy appearance compared to most other beetle larvae.

According to Dermestidae taxonomy records, larval Dermestids range from 5-15 mm in length and are typically covered in tufts of long, dense hairs. In the case of D. ater, the larva’s body is whitish except for its darker head capsule and dorsal plates, which darken to black, brown, or reddish as the larva matures. At the posterior end, the larva bears two spine-like appendages called urogomphi, which are a useful identification feature under magnification.

Signs of Dermestes beetle infestation 🔗

Dermestes beetles primarily damage stored cocoons, silkworm pupae, and grainage rooms. The female beetle lays eggs in the floss (the outer silk layer) of cocoons. Once hatched, the larvae bore through the silk layers to feed on the pupa inside. As documented in sericulture entomology literature, both larvae and adults feed on silk pupae, piercing freshly spun, stored, or stifled cocoons and making them unreelable – meaning the silk thread can no longer be unwound.

The adult beetles are also known to migrate from cocoon storage areas into grainage rooms, where they attack the abdominal region of adult moths. A published study in the Journal of Stored Product Research identified 28 dermestid species associated with the silk industry globally, confirming that D. ater and related species are serious, widespread pests of silkworm cocoon storage. Damage by Dermestes larvae is visible as multiple small, round borehole entry points across the surface of infested cocoons – a pattern quite different from other storage pests.

Comparing the two pests at a glance 🔗

The Uzi fly and the Dermestes beetle differ not only in their physical appearance but also in when and where they cause damage. The Uzi fly is an endoparasitoid – it attacks living silkworm larvae during the active rearing phase and kills them from the inside out. The Dermestes beetle is a stored-product pest – it targets cocoons and pupae after harvest, during storage and processing.

Both pests, however, share one critical trait: early identification dramatically improves the chances of controlling them before significant economic loss occurs. The Uzi fly is identified by its larger size relative to a housefly, blackish-grey coloration, and distinct black stripes on the thorax and abdomen. The Dermestes beetle is identified by its black, elongate-oval body and, in its larval stage, by the dense covering of long, dark bristles that make it look distinctly hairy among stored cocoons.

Recognizing the egg scars on silkworm larvae or the cocoon exit holes for the Uzi fly, and the boreholes in stored cocoons for Dermestes larvae, gives sericulturists the early warning needed to act before an infestation spreads through an entire rearing batch or storage facility.

What do you think? If you were inspecting a silkworm rearing house and spotted a fly slightly larger than a housefly with a striped abdomen, would you know what steps to take next? And how do you think the two-stage threat – one pest targeting living larvae and another targeting stored cocoons – changes the way a sericulturist should plan their crop protection strategy?

References

1. https://link.springer.com/chapter/10.1007/978-981-10-3304-9_9
2. https://link.springer.com/article/10.1023/A:1012982030848
3. https://www.britannica.com/animal/tachinid-fly
4. https://silks.csb.gov.in/parbhani/diseases-and-pests-of-silkworms/
5. https://en.wikipedia.org/wiki/Dermestes_ater
6. https://en.wikipedia.org/wiki/Dermestidae
7. https://www.notesonzoology.com/sericulture/4-major-enemies-of-silkworm/319
8. https://www.sciencedirect.com/science/article/abs/pii/0022474X95000323