Pest Management in Eri Silkworm Rearing

Eri silkworms (Samia ricini) are central to India’s non-mulberry silk industry, especially across northeastern states like Assam, Meghalaya, and Nagaland. While disease management in eri culture gets a lot of attention, predators operating right inside the rearing house can be equally destructive. Ants, cockroaches, rats, and lizards target eri silkworms at nearly every stage – from eggs and early-instar larvae to spinning worms and cocoons. Without active pest management, these predators can silently wipe out significant portions of a rearing batch. This post covers the key predators found in eri silkworm rearing, the specific damage they cause, and the practical steps to control them.

Why predators are a serious concern in eri silkworm rearing 🔗

Unlike diseases, predators cause direct, immediate losses. A single overnight rat incursion or an ant trail into a rearing tray can destroy dozens of larvae before morning. Eri silkworms are the only fully domesticated non-mulberry silkworm, which means they are reared entirely indoors on trays and containers – environments that can attract a range of opportunistic predators if hygiene and structural safeguards are not maintained. The predators covered here fall into two categories: insect pests (ants and cockroaches) and vertebrate predators (rats and lizards).

Insect predators 🔗

Ants (Oecophylla smaragdina) 🔗

The red weaver ant, Oecophylla smaragdina, is among the most damaging insect predators in silkworm rearing environments. This highly aggressive species is an active forager known to attack and kill early larval instars of silkworms, making younger, more vulnerable eri larvae particularly at risk. Ants do not just kill on contact – they also carry away silkworm eggs from rearing trays, directly reducing the number of larvae that hatch and disrupting rearing continuity.

What makes ant infestations especially problematic is their organised, colony-based foraging. Research on muga silkworm rearing in Assam found 100% ant infestation incidence during rearing seasons, with O. smaragdina identified as the dominant predatory species causing an estimated 1-25% crop loss. Given that eri silkworms are reared in similar indoor environments in the same region, the risk is equally significant.

Control measures for ants:

• Ant wells: Placing the legs of rearing stands in containers filled with water mixed with kerosene – commonly called ant wells – is the primary mechanical control. Ants attempting to climb the stand legs are repelled or trapped in the liquid barrier.
• Ash or kerosene barriers: Applying ash or kerosene at the base of mountages (spinning structures) during the spinning stage deters ant entry at critical periods.
• Pre-rearing chemical treatment: Spraying a 2% Rogor solution around the rearing area at least 15 days before rearing begins helps reduce resident ant populations. Ant nests in or around the rearing house should be located and destroyed well before the rearing cycle starts.
• Raksha Rekha: This chalk-based repellent barrier drawn around the rearing stand legs is a simple and effective deterrent against ant entry.

Cockroaches (Periplaneta americana) 🔗

The American cockroach, Periplaneta americana, is an omnivorous scavenger that thrives in warm, humid environments – exactly the kind of conditions maintained in silkworm rearing rooms. This species is reddish-brown, averages about 4 cm in length, and is highly active at night, which is precisely when it causes the most damage in rearing rooms. Cockroaches feed on silkworm eggs, young larvae, and organic rearing waste, and their nocturnal activity makes early detection difficult.

Beyond direct predation, cockroaches are a hygiene hazard. They are known to transmit pathogenic microorganisms, which can contaminate feeding leaves and rearing surfaces, compounding losses beyond what direct feeding alone would cause.

Control measures for cockroaches:

• Sanitation: Removing decaying organic matter, maintaining dry floors, sealing cracks in walls and floors, and keeping the rearing room free of food scraps are the most effective first-line controls. Cockroaches are strongly attracted to moisture and organic waste.
• Exclusion: Sealing entry points such as gaps around pipes, door frames, and vents prevents cockroach ingress. Mesh screens over ventilation openings help without compromising airflow.
• Trapping: Sticky traps or bait traps placed along walls and in corners where cockroaches travel can significantly reduce their numbers without requiring pesticide use inside the rearing room.
• Periodic fumigation: In heavily infested rearing houses, fumigation between rearing batches – when silkworms are not present – can eliminate cockroach populations before the next cycle begins.

Vertebrate predators 🔗

Rats (Rattus rattus) 🔗

The black rat, Rattus rattus, is one of the most destructive vertebrate predators in indoor silkworm rearing. Rats consume silkworms across all life stages, typically avoiding only the silk glands, and will bite open cocoons to access pupae. A single rat can destroy large numbers of larvae and cocoons in one night, and their chewing behaviour damages rearing equipment as well.

Rats are especially drawn to rearing houses because of the consistent availability of food in the form of larvae, feed leaves, and organic waste. Their rapid reproduction means that even a small initial presence can escalate into a serious infestation within weeks if left unaddressed.

Control measures for rats:

• Wire mesh proofing: Installing wire mesh over windows, doors, and any holes or openings in the rearing room is the most reliable structural control. Mesh should be fine enough to prevent rat entry while still allowing ventilation.
• Snap traps and cage traps: Mechanical traps placed along walls and in corners where rat activity is observed are effective and safe to use inside rearing facilities. Traps should be checked and reset daily.
• Rodenticide baits: Bait stations can be placed outside the rearing house or in areas inaccessible to silkworms. Anticoagulant rodenticides in secured bait stations are commonly used, but placement must be strictly controlled to avoid any contact with rearing areas or feed plants.
• Eliminating harborage: Removing clutter, stacked boxes, and debris from inside and around the rearing house eliminates hiding and nesting sites that rats use to establish themselves near the rearing area.

Lizards (Hemidactylus flaviviridis) 🔗

The yellow-bellied house gecko, Hemidactylus flaviviridis, is a common resident of rural buildings across tropical India. While geckos are generally considered beneficial as insect predators in other settings, they become a direct threat inside silkworm rearing rooms. Lizards frequently enter rearing houses and prey on young-instar larvae, picking them off rearing trays and causing considerable damage. They are attracted by the concentration of soft-bodied larvae, which are easy prey.

Lizards are particularly active during the night and in the early morning hours, coinciding with cooler temperatures when silkworm larvae are less active on the rearing trays. Young larvae in the first and second instars are the most vulnerable since they are small, slow-moving, and clustered on trays.

Control measures for lizards:

• Exclusion: The rearing room should be kept free from lizards by sealing wall cracks, gaps near ceiling joints, and openings around pipes where geckos enter and hide during the day.
• Netting: Fine mesh netting over rearing trays or across doorways provides a physical barrier that prevents lizards from accessing larvae directly.
• Repellents: Placing naphthalene balls or tobacco leaves near entry points deters geckos. Some rearers use phenyl-based repellents along the base of walls. These should be positioned carefully to avoid any direct contact with larvae or feed leaves.
• Manual removal: Regular inspection of the rearing house before and after each rearing session allows for the physical removal of any lizards found inside.

Integrated pest management: the foundation of predator control 🔗

No single measure works in isolation. Effective predator management in eri silkworm rearing is built on a combination of structural safeguards, consistent hygiene, and timely monitoring. The key principles are:

• Maintain cleanliness: Regular removal of rearing waste, dead larvae, and leftover leaves eliminates the organic material that attracts cockroaches, rats, and other scavengers. Rearing appliances should be washed and dried between batches.
• Inspect before rearing: Checking the rearing room for ant trails, cockroach activity, rat droppings, and gecko presence before each batch begins allows problems to be addressed before silkworms are placed in the room.
• Proofing the rearing house: Wire mesh on all openings, sealed wall cracks, and tight-fitting doors form the first line of defence against both vertebrate and insect predators.
• Avoid pesticide use during rearing: Eri silkworms are highly sensitive to chemical residues. Any chemical pest control – whether for ants, cockroaches, or rodents – must be completed well before rearing begins and all treated surfaces must be thoroughly cleaned before larvae are introduced.

The Central Silk Board of India recommends maintaining strict sanitation and structural hygiene as the cornerstone of predator management in all types of silkworm rearing, including eri culture. These principles, applied consistently across rearing cycles, significantly reduce predator pressure without relying heavily on chemical interventions.

Summary of predators and their controls 🔗

To recap: ants (Oecophylla smaragdina) attack larvae and eggs in rearing trays and are controlled primarily using ant wells, barriers, and pre-rearing chemical treatment. Cockroaches (Periplaneta americana) damage eggs and young larvae overnight and are managed through sanitation, exclusion, and trapping. Rats (Rattus rattus) are the most destructive vertebrate predator, consuming larvae and cocoons at all stages, and are controlled through wire mesh proofing, traps, and bait stations outside the rearing area. Lizards (Hemidactylus flaviviridis) target young larvae and are kept out through room sealing, fine mesh netting, and repellents. Together, these measures form a practical predator management framework that every eri silkworm rearer should implement as part of standard rearing practice.

What do you think? Given that eri silkworms are reared entirely indoors, do you think structural proofing alone is sufficient to control vertebrate predators, or should chemical repellents play a larger role? And of the four predators covered here, which do you consider the hardest to manage in a small-scale rearing setup – and why?

References

1. https://en.wikipedia.org/wiki/Eri_silk
2. https://www.intechopen.com/chapters/61673
3. https://journalijpss.com/index.php/IJPSS/article/view/4905
4. http://sericulture-activities.blogspot.com/2017/10/silkworm-pests.html
5. https://ask.ifas.ufl.edu/publication/IN298
6. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/periplaneta-americana
7. https://acvcsd.org/programs-services/cockroaches/american-cockroach/
8. https://www.notesonzoology.com/sericulture/4-major-enemies-of-silkworm/319
9. https://silks.csb.gov.in/churchandpur/diseases-and-pests-of-silkworms/