A jar trap works: put bait in a smooth-sided glass jar, coat the inside of the upper wall so roaches cannot climb back out, and set it flat against a wall where roaches forage. This is a real design from the research literature. Purdue entomologists Changlu Wang and Gary Bennett used a 124-milliliter baby food jar baited with white bread and beer, with the inner upper surface coated in a 2:3 mix of petroleum jelly and mineral oil, and compared it head to head with seven commercial sticky traps (*Environmental Entomology*, 2006). The jar caught roaches. It also caught far fewer than the best sticky trap, and it was "strongly biased for sampling adult cockroaches," missing most of the nymphs. Use a jar trap to find out where roaches are and whether your control is working. Do not use it as the control. UC IPM is blunt about that division of labor: sticky traps and monitors are for detection, and "insecticide sprays alone will not eliminate cockroaches" either. Baits are the primary control tool.
The earlier version of this article got three things wrong. It told readers to put a sugar-and-boric-acid mixture in the jar, which turns a monitoring device into an unsecured open container of pesticide, contrary to the placement instructions on consumer boric acid labels. It said to pick baits with "a strong scent that will draw them in from a distance," when Rust and Reierson found German cockroaches are not attracted to these foods beyond a few centimeters. And it recommended cucumber slices and bay leaves as repellents, which the extension and peer-reviewed sources we reviewed do not support. This version drops all three.
Why The Jar Design Works At All
Two pieces of roach anatomy do the work.
Roaches climb using tarsal claws for rough surfaces and soft adhesive pads called arolia for smooth ones. Clean vertical glass defeats the claws, and a greasy film defeats the pads by giving them nothing to wet-stick to. That is the whole mechanism: a one-way door made of physics rather than adhesive.
Species matters here. Virginia Tech Extension notes that unlike other pest roaches, "oriental cockroaches cannot climb up smooth surfaces (they lack sticky pads on their feet)". A bare glass jar will hold oriental cockroaches reasonably well on its own. German and American cockroaches are better climbers, and lightweight nymphs of both are better still, which is exactly why the barrier coating is not optional and why the jar still under-catches small nymphs.
The second piece is that roaches are contact foragers over short distances. Wang and Bennett summarize the earlier work plainly: research "has shown that German cockroaches are not attracted to the food or scents discussed above over a few centimeters." A jar trap does not pull roaches across a room. It intercepts roaches that were already walking past it. That single fact determines everything about placement.
How To Build One
You need a glass jar with smooth interior walls, a barrier material, and bait.
- Pick the jar. Small is fine and easier to place. The research designs range from a 124-milliliter baby food jar to a one-quart wide-mouth mason jar. Straight or slightly tapered sides work; heavily ridged or embossed glass gives the claws purchase.
- Give them a ramp in. Wrap masking tape, paper tape, or a strip of rough cardboard up the outside of the jar so roaches can reach the rim. Without it the trap catches almost nothing, because they cannot climb the outside either.
- Coat the inside of the upper wall. Spread a thin film about two inches deep down from the rim. Petroleum jelly alone works; the Purdue trap used petroleum jelly thinned with mineral oil at a 2:3 ratio, which spreads more evenly and stays slick longer. Researchers have also used plain grease or a dusting of clay powder. Keep the coating off the rim's outer edge so it does not collect lint.
- Bait the bottom. White bread moistened with beer is the best-documented bait for this device. Wang and Bennett found bread with beer increased trap catches 34-fold over an unbaited trap, well ahead of peanut butter, commercial lures, and gel bait. Ebeling and Reierson had reported in 1974 that white bread alone increased jar trap catches 7.6-fold. Other researchers have caught German cockroaches in jar traps using banana peel and boiled raisins.
- Set it flat against a wall, upright, with the taped side touching the wall.
Two practical notes. Bread and beer dries out and molds quickly in an open container, so plan on refreshing it every two or three days. And do not add any insecticide to the bait. The value of this trap is that it is a nontoxic counting device you can place in a kitchen with a toddler in it.
Where To Put It, And For How Long
Placement is the whole game, because the effective radius is a few centimeters.
- Floor-to-wall junctions. UC IPM says the best trap sites are "at the junctions of floors and walls and close to sites where cockroaches are suspected."
- Behind and beneath appliances. Refrigerator, range, dishwasher, and the warm motor compartments behind them.
- Under the kitchen and bathroom sinks, where plumbing penetrations meet moisture.
- Inside lower cabinets, especially near hinges and back corners.
- Wherever the evidence already is. Look for dark fecal specks and smears, cast skins, and empty egg cases. Those marks indicate harborage, and traps near harborage catch more.
Penn State Extension's framing is useful: traps "will tell you where 'hot spots' are." Put out several at once rather than one, number each jar, and write down the count and the date. One trap gives you an anecdote; six give you a map. Our guide to how many roach traps you need walks through a workable grid for a typical apartment or house.
Check daily for the first several days. UC IPM notes that "many times, cockroaches will be caught within the first 24 hours of placing a trap." After that, a weekly check with fresh bait is enough, and the number you want to watch is the change from week to week, not any single night's total. If you want context on how fast different trap types register a population, see how long roach traps take to work.
How To Read The Catch
The count is one signal. The composition of the catch is a better one.
UF/IFAS Extension's assessment-based guidance reads trap contents this way: "One to a few adults indicates that you are most likely dealing with a new introduction," while "the presence of all life stages of German cockroaches is an indication that you are dealing with an established infestation." A cluster of early-instar nymphs tells you to search hard within five to ten feet of that trap, because tiny nymphs do not travel far from harborage.
Here is the jar trap's specific weakness. Wang and Bennett concluded the baby food jar trap "is strongly biased for sampling adult cockroaches." In their kitchen trials, sticky traps returned nymph fractions of 0.69 to 0.84, roughly consistent with the real population structure in infested homes, where nymphs make up about three quarters of German cockroaches. Robinson and colleagues, sampling apartments with quart mason jars baited with boiled raisins, recorded a nymphal ratio of only 28 percent. A jar trap will therefore make an infestation look smaller and older than it is. If your jars catch a steady trickle of adults and no nymphs, do not conclude there are no nymphs; if you need an accurate age breakdown, run commercial sticky traps alongside the jars.
On raw catch numbers the jar also lost. In the 1-square-meter arena test, relative catch across the eight traps ran 78 for the best sticky trap down to 3 for the jar and 1 for the worst sticky trap. In the simulated kitchens the spread narrowed to 36 for the best and 7 for the jar. Cheap, reusable, and nonlethal are genuine advantages for repeated sampling. Sensitivity is not one of them.
What A Jar Trap Will Not Do
It will not reduce the population. Wang and Bennett state it directly: "Sticky traps are not suitable for controlling German cockroach infestations," and the jar caught a fraction of what those sticky traps caught. The population foraging at night is a minority of the population in the wall void and under the appliance, and reproduction continues there. Removing a dozen adults a week does not outrun that.
It also will not identify the species by itself, and species drives the treatment plan. UC IPM stresses that you "must first determine which species is present and where they are located." Trapped specimens are useful for exactly this, so photograph one before disposal. Small tan roaches with two dark stripes behind the head are German cockroaches, an indoor breeding population. Large reddish-brown ones are usually American cockroaches, often arriving from drains, crawl spaces, or sewers. Glossy near-black ones that stay low and damp are oriental cockroaches.
What Actually Reduces The Population
Once the traps have shown you where the activity is, put control where the traps are hottest.
- Gel bait in cracks and crevices. UC IPM calls bait products "the primary pesticides used to treat cockroach infestations" and notes gel baits "are very effective when placed in or near locations where cockroaches harbor or forage." Small dabs, many of them, inside cabinets, along hinges, behind appliances, and in voids. Our walkthrough of how to use Advion roach gel correctly covers dab size and placement density straight from the label.
- Remove competing food. UC IPM warns that if roaches "have access to food, baits (which are primary control tools) may take longer to provide satisfactory control." Clean grease films behind the range, seal food containers, take trash out nightly, and pick up pet bowls overnight.
- Fix the water. Eliminate plumbing leaks, dry the sink cabinet, and ventilate where condensation collects.
- Vacuum. UC IPM notes that vacuuming cracks and crevices "removes cockroaches, shed skins, and egg cases, reducing overall cockroach numbers," and recommends a HEPA or triple-filtered machine because droppings and shed skins are allergens.
- Seal and exclude. Door sweeps, weather stripping, caulk at pipe penetrations, and inspection of anything coming in from storage.
- Skip the foggers and broadcast sprays. Penn State Extension is direct: "Avoid using foggers and sprays. You can't control where the chemicals go, and the risk of exposure is high. Sprays and foggers may also irritate lungs." A 2013 practice parameter in the Journal of Allergy and Clinical Immunology reached the same conclusion for homes with asthma, favoring low-toxicity gels and crack-sealed dusts over sprays.
For the full sequence in order, see our step-by-step plan for getting rid of roaches.
Safety Notes
Do not put boric acid, baking soda mixtures, or any pesticide in the jar. Boric acid works as a thin, dry, undisturbed dust in voids, not as a wet slurry in an open jar, and NPIC notes that "many boric acid products require that they be applied in places out of children's reach." Putting it in a bait cup on the floor is the opposite of that. If you want to use boric acid, use it as labeled; our guide on how long to leave boric acid down explains the realistic timeline.
Glass on the floor. A jar in a doorway or a dark hallway is a trip and breakage risk. Keep them tight against walls and out of traffic paths.
Allergens are the main documented household health concern. Cockroach allergen is a well-established driver of childhood asthma morbidity in urban homes, and the practice parameter cited below recommends that "reservoirs of cockroach contaminants should be cleaned or removed to prevent additional exposure to occupants." Wash surfaces and vacuum with a filtered machine rather than dry-sweeping droppings.
Disposing Of What You Catch
The jar is nonlethal by design, which helps for counting and complicates disposal. Cap it, count and photograph the contents through the glass, then seal it in a plastic bag and put it in an outdoor bin. UC IPM gives the same advice for sticky traps: seal in plastic, then trash. If you would rather not handle live insects, add an inch of soapy water under the bait. Wash your hands and the jar afterward.
The previous version of this article described freezing the jar as a "humane" method. We found no source establishing that, so we are not asserting it.
DIY Or Call A Pro
Jar traps are a reasonable DIY step in every case, because information is always worth having. The control question is separate.
Handle it yourself when trap counts are low and static, you have one clear hot spot, the species is American or oriental cockroach coming in from outside, and gel bait plus sanitation is bringing the numbers down within a few weeks.
Call a licensed professional when your traps show all life stages of German cockroach, when counts are flat or rising after 30 days of correct baiting, when roaches are visible during the day, when activity spans multiple rooms or appliance motors, or when someone in the home has asthma. UC IPM notes that "for serious indoor infestations and other large or complex cockroach problems, professional pest control services are often required."
In an apartment or condo, involve building management early regardless of how your own unit looks. Roaches move through shared plumbing chases and wall voids, and unit-by-unit treatment fails when the neighboring unit is untreated. Our guide on what to do when neighbors have roaches covers how to document the problem and what landlords are typically obligated to do.
Frequently Asked Questions
Does a jar trap actually catch roaches?
Yes. It is a documented research design, and in controlled comparisons it caught roaches consistently. It simply caught fewer than good commercial sticky traps and skewed heavily toward adults. Treat a catch of zero as weak evidence and a catch of many as strong evidence.
What is the best bait to put in the jar?
White bread moistened with beer has the strongest support. In the Purdue kitchen trials it outperformed peanut butter, two commercial lures, and a gel bait, raising catches 34-fold over no bait. Banana peel and boiled raisins have also been used successfully in published jar-trap studies. Replace it every two or three days before it dries or molds.
Can I skip the petroleum jelly?
Only for oriental cockroaches, which cannot climb smooth surfaces. German and American cockroaches, and especially their lightweight nymphs, can climb clean glass well enough to leave. The greasy band is what makes the jar one-way.
How many jars should I set out?
More than one. The trap only intercepts roaches that walk within a few centimeters of it, so coverage matters more than any individual trap. Six to twelve placements in a kitchen and bathroom gives you a usable map; a single jar tells you almost nothing about where the population is.
Will jar traps get rid of an infestation?
No. Trapping removes a small, adult-skewed slice of the foraging population while reproduction continues in harborage you cannot reach. Use the traps to target gel bait, sanitation, and exclusion, and judge those efforts by whether the trap counts fall.
Why am I catching only large roaches and no small ones?
That is the known bias of this trap design, not necessarily a fact about your home. Nymphs typically make up around three quarters of a German cockroach population, but jar traps catch them poorly. If the age breakdown matters, run commercial sticky traps alongside the jars.
Is a jar trap safe around kids and pets?
As built here, with food bait and no pesticide, it is among the lowest-risk options available. The risks are broken glass and a pet eating the bait. It stops being low-risk the moment you add boric acid or any other insecticide to it, which is why we recommend against that.
Sources
- Wang and Bennett, "Comparison of Cockroach Traps and Attractants for Monitoring German Cockroaches," *Environmental Entomology* 35(3):765–770 (2006) — the jar trap specification and barrier mix, relative catch versus seven sticky traps, the adult sampling bias, the 34-fold effect of bread with beer, the Ebeling and Reierson 7.6-fold figure, Robinson's 28 percent nymphal ratio, and the few-centimeter attraction range.
- UC IPM Pest Notes: Cockroaches (PDF) and the UC IPM cockroach overview — trap placement, daily checks, identifying species first, baits as the primary control tool, HEPA vacuuming, disposal, boric acid behavior, and when to hire a professional.
- UF/IFAS Extension ENY-989: Assessment-Based Pest Management of German Cockroaches — how to read monitor contents and the search radius around early-instar nymphs.
- Virginia Cooperative Extension: Oriental Cockroach — oriental cockroaches lack adhesive foot pads and cannot climb smooth surfaces.
- Penn State Extension: Got Roaches? Eliminate Roaches with IPM — traps as hot-spot finders, gel bait placement, and the warning against foggers and sprays.
- Portnoy et al., practice parameter on cockroach exposure reduction, *Journal of Allergy and Clinical Immunology* 132(4), 2013 — monitoring with sticky traps, IPM effectiveness, gels over sprays, and cleaning allergen reservoirs.
- UF/IFAS Extension ENY-2030: Do-It-Yourself Insect Pest Traps — homemade trap guidance and the caution that traps alone may not manage persistent infestations.
- NPIC: Boric Acid General Fact Sheet — toxicity to people and pets, children's sensitivity, and label requirements to apply out of children's reach.
