By: Pat Hottel, B.C.E.

One way to characterize the types of pests that are likely to infest a food-processing facility is by the products produced. In this article we will cover the most common pests and most vulnerable locations for those pests in wet-processing plants. Examples of wet-processing plants include those that produce beverages, canned goods, dairy products and frozen foods. They typically will utilize water in processing and clean-up and water is a key factor in the profile of pests that infest the site.

Pests will have certain food preferences and essential environmental needs for survival. When those conditions are met, pests thrive. Liquid-processing facilities share certain environmental profiles and we can predict pests on those commonalities. Sanitation, employee practices, facility processes, and structural and equipment design can be used to manage these potential risks. In addition, not all areas within a facility will meet the needs of the pest equally and certain areas will have a lower risk for pest development. Here is a list of the 10 most common areas of pest activity by product type, structural design and practices. Utilize this list in prioritizing areas for inspection and monitoring as part of a pest prevention program. We can assign these areas/conditions for inspection as pest vulnerable zones (PVZs).

1. Floors

Because copious quantities of water, water under pressure and caustic cleaners may be used in cleaning programs, floors in wet processing facilities take a beating. Floor coatings and tile grouting can wear away, allowing for food and moisture to pocket in deteriorating floors. Floor repairs can be expensive, but floor integrity must be maintained. Water and food particles also can sift into wall voids via floor/wall junctures if junctures are not properly sealed. Coving of floors along the wall/floor intersect help reduce this problem. If moist organic debris remains, small flies such as Drosophila flies and phorid flies can develop.

2. Floor Drains

Extensive drainage systems are needed to handle the large quantities of water used on site. Floor drains will be numerous with channel drains or trench drains often present. Floor drains can be complicated in design and allow for areas of organic material to accumulate. Improperly designed drainage systems can be responsible for major issues with small flies and other insects. Channel drains can be particularly problematic in that they are more likely to retain moisture and debris. Proper pitch of the channel drain is needed to help ensure water and debris drainage. Channel drains also present a larger surface area at the drain/floor junctures for deterioration of the flooring. As mentioned previously, deteriorating floors can mean areas for water and food debris to accumulate.

Drains, especially when the water trap is not maintained, can be a pathway for drain flies and American cockroaches to enter a facility. It is an underground passageway for pests that inhabit sewer systems to find entry. Special one-way valves that allow water to flow downwards but excludes pests from coming into the site may be used. Proper grates that permit removal by staff for cleaning can help exclude cockroaches. Square grid grates are available for this purpose.

Lastly, major fly infestations can be tied to sub slab pipe breaks and as the facility ages, this can be a major concern. Sub-slab issues will require areas of flooring to be removed to remove soil and make pipe repairs. This is costly from the standpoint of labor costs and materials and also downed production time.

3. Dumpster/Compactor Areas

If we ranked the areas listed in this article by their level of importance, the dumpster/compactor area would be No. 1. Odors emanating from trash can attract a variety of pests towards the building including rodents, filth flies and birds. Odors attract and food availability encourages the pests to stay. If dumpster pads and the interior of the dumpster box are not cleaned regularly, flies can lay eggs and maggots will develop in the moist food residues.

Pests also can be transported from one site to another if dumpster boxes are not assigned to one site. Food plant staff and/or the waste hauler should be delegated the task of cleaning the interior of the dumpster and pad when garbage pick-up occurs. Seasonality and weather may dictate feasibility. The dumpster pad should be checked regularly for cracks and surface integrity. Repairs should be made, as needed, to eliminate crevices where moist organic waste can accumulate.

Special attention to pest proofing the structure in and around the dumpster is critical since pests will be attracted to this area. All chutes, doors and walls should be well sealed to prevent pests that have been attracted to the area from entering the building.

4. Trailers for Repurposing Food/Waste

Americans waste a lot of food and the repurposing of food for animal feed or other uses makes sense. The same is true of empty packaging materials. Food processors may have zero waste programs and even recycle items like hair nets and disposable smocks. All these programs are beneficial but the potential for pest attraction must be understood and the correct preventive steps put in place.

It is not uncommon to see trailers used for baled cardboard to be staged at an open dock door. Despite seals around where the trailer meets the door, there are often gaps left at the area where the dock plate ramp bridges to the trailer. This can provide a large pest-vulnerable opening for rodents, birds, insects and nuisance wildlife. Although easy access for staff to load trailers is needed, the best practice is to keep doors closed when not actively loading. Roll-top doors for trailers are preferred over doors that swing outward. Outward-swinging doors cannot be closed while the trailer is backed up to the dock.

If chutes are used for food wastes, the chutes must be checked for any pest proofing needs and should be placed on a regular cleaning program. The area where the chute connects to the trailer should fit tightly to prevent birds, rodents and wildlife from accessing the food. Trailers used for food wastes, just like dumpsters, should have a cleaning regimen. Trailers should be inspected for pest activity. Pests like rodents can arrive at food facilities on trailers used for repurposing food.

5. Roofs

Roofs can be one of the most overlooked areas for pest activity. Pests may be attracted to the area for warmth and shelter. Stinging insects may establish nests along eaves or other secluded areas. Ponding of water on roofs can provide moisture sources for pests and developmental sites. Although weekly service is not normally needed, at least quarterly inspections of the area are advised. This frequency can be adjusted based on conditions, seasonality and historical pest pressures.

6. Bulk Unloading

Not all sites will have a bulk unloading system but when a liquid processing plant does, it generally involves corn syrup. This sweet substance can attract honeybees, yellowjackets and other wasps. Keeping the area as clean as possible and reducing leaks in the system will be essential in helping to manage the risks. The area should be added to the inspection list at least seasonally.

7. The Packaging Difference

Certain types of packaging are more likely to be damaged during storage than others. Pop top tabs on cans and soft, juice box-type containers are subject to greater damage. Phorid flies can be issues in wet pet food cans and soups like chili, if cans get damaged and go undiagnosed. How the manufacturer boxes and stacks these items on a pallet also will make a difference. Protecting the cans from forklift mishandling is a plus. Knowing the products and risks and assigning inspection time to these areas is important.

8. Corrugated Wall Construction & FRP

Metal corrugated walls are a common building construction material but are subject to damage from forklifts and are more difficult to pest proof and keep sealed. Damaged walls may provide pests access from the exterior and harborage on the interior. In some facilities, rolled and laminated insulation is placed over the corrugate wall for temperature control. This practice makes it a perfect location for rodents to travel and nest.

Fiberglass reinforced panel walls are often used due to cleanability and moisture resistance characteristics. However, over time these panels can loosen from walls and create harborage sites for German cockroaches. It may be difficult to effectively apply insecticides into the cracks and openings. Walls must be checked and pest proofed on a routine basis.

9. Break Rooms/Locker Rooms

There are several pests that will hitchhike on employees’ belongings. These include the German cockroach and the common bed bug. Areas where employees eat and store their personnel belongings can see insect activity. Strict policies regarding the storage of these items in designated areas must be adhered to by food plant staff. Regular locker cleanouts and policies of removing lunch containers from break rooms at ends of shifts must be established and followed. Use of reach in coolers in break rooms for storing lunches can help reduce issues with cockroaches. Both locker rooms and break rooms should be monitored by the pest management professional.

10. Floor Scrubber Areas

The moisture and organic material from equipment wash down bays and floor scrubber units may support pests like flies. Improperly stored and maintained wet vacs, mops and mop buckets are another potential issue. The drains, floors and walls in the wash bays must be cleaned and maintained.


Pat Hottel, B.C.E., is the technical manager for McCloud Services. She has over 40 years of pest management experience and is a member of the National Pest Management Association’s Fumigation Committee. 

This Tech Talk article was originally published in the July 2021 edition of PCT magazine.