How to Set Snap Traps Along a Rodent Runway

Why this matters

A snap trap is the cheapest, fastest, most certain tool a rodent tech carries, and the one most often wasted. Two traps baited with a glob of peanut butter and set out in the middle of the garage floor catch nothing, and the customer concludes the mice are too smart. Rodents run edges and they run the same edges every night. A trap that sits square on a runway, oriented so the animal crosses the trigger in its normal stride, catches on the first night; a trap a foot off the line mostly does not. This card owns finding the runway and setting traps on it. How far apart and how many, which depends on species and foraging range, is owned by 'Mouse and Rat Foraging Range and Trap Spacing'.

Protection, for you and for the household

Gloves on for the whole job. Droppings, urine and dead rodents carry disease, and dried droppings disturbed in a closed space can be inhaled. Do not sweep or blow droppings; follow 'Rodent Droppings and Hantavirus for the Trades' for cleanup and respiratory protection. Gloves also keep your scent off the trap, which matters more for rats than mice.

Set the bar with your fingers clear of the jaw path. Rat-size snap traps break fingers. Arm the trap with your hand behind the striker bar, place it by holding the sides of the base, and never reach across an armed trap. On a plastic trap with an expanded trigger, press it open from the back.

Children, pets and non-target animals. Any trap a child or a dog could reach goes inside a tamper-resistant cover or box, behind an appliance, or out of reach. Ask about pets before you place anything. A dog with a rat trap on its nose is the call that ends the account.

Finding the runway

The runway is where the animal actually goes, not where you saw it. Read it from sign:

• Droppings. Mouse droppings are small, roughly 1/8 to 1/4 in, rod-shaped with pointed ends, scattered along the route. Rat droppings are much larger, on the order of 1/2 in or more, and often in groups. Concentrations mark where the animal pauses: corners, behind appliances, at an entry hole.
• Rub marks. A dark, greasy smear along the base of a wall, around a pipe or on the edge of a hole, from fur oil. Rat rub marks are obvious; mouse marks are faint and need a low flashlight angle.
• Tracks and tail drags in dust. Lay a thin dusting of talc or flour on a suspected route overnight if you need proof, on a floor where it can be cleaned up.
• Gnaw marks and entry holes. A mouse can pass an opening of about 1/4 in and a rat about 1/2 in. A hole that size with rub marks around it is the start of a runway.
• Urine stains under a UV light, if the shop carries one.

Look along wall bases, behind and under appliances, along the top of the foundation in garages and basements, along pipe runs, and at the junctions where a runway leaves one wall for another. For signs beyond these, see 'Pest Activity Signs Reference'.

The three sets

 PLAN, WALL ALONG THE TOP
 ========================================== WALL
 |T|       <T==T>                 <T==T>
 |b|       pair, back to            |b|
 |b|       back, triggers           |b|  stem
 single,   out along the            |T|  trigger
 trigger   wall both ways            ^   away from
 to wall                          runway out from
                                  under the range
 T = trigger end   b = base

Single, trigger to the wall. The trap sits perpendicular to the wall with the trigger end touching it. An animal running the wall in either direction has to step on or across the trigger. This is the default set on a straight run with one trap.

Back-to-back pair. Two traps parallel to the wall, end to end, triggers facing out in opposite directions. Whichever way the animal comes, it meets a trigger head-on, and an animal that jumps one trap often lands on the other. Use it on a well-used run where you want to catch the first night.

T where runways meet. Where a runway leaves the wall, for example from under the range or at the end of a cabinet run, set a back-to-back pair along the wall and a third trap as the stem, lying along the incoming runway with its base against the middle of the pair and its trigger facing away from the wall toward the animal coming out. That covers both directions along the wall plus the cross route.

The steps

1. Map the runways before setting anything. Walk the space with a flashlight, mark sign on a sketch, and decide where the runways are and which species you have. The species decides spacing and the bait plan.

2. Decide baited or unbaited, and pre-bait for rats. Mice are curious and will investigate a new object on their route; set traps armed from the first night. Rats are wary of new objects, so many programs place traps unarmed and baited for a few nights first, then arm them once the bait is being taken. A trap squarely on a heavy runway can work unbaited, especially with an expanded trigger. Use a small amount of a food bait pressed into the trigger cup, or nesting material such as cotton for mice in cold weather. A big glob lets the animal lick it off without tripping the trigger.

3. Set the traps on the line, with gloves on. Place each trap so the trigger is in the animal's path, tight to the wall. A trap two inches off the wall is off the runway.

4. Use enough traps. One trap per runway is a sample, not a treatment. Set several close together on mouse runways, at the spacing and count in 'Mouse and Rat Foraging Range and Trap Spacing'; set rat traps on the main runs, fewer but heavier.

5. Number the traps and record each location on the sketch and the service record: trap number, set type, bait, and where it sits. Without numbers you cannot tell which positions are working, and a trap nobody recorded is a trap nobody checks.

6. Check on a schedule and record every check. A common start is the next day, then every few days while catches continue, and never longer than the service interval the customer agreed to. A dead rodent left in a trap for a week becomes an odor and fly problem. At each check, record catches by trap number, re-bait or reset, and move a trap that has caught nothing for a couple of checks, with no fresh sign near it, onto a runway that shows fresh sign.

7. Remove captures with gloves, bag them, and dispose of them per local rules. Disinfect the trap if it is going back into service.

Worked example: mice in a kitchen next to an attached garage

The call. Droppings in the silverware drawer and under the sink, scratching at night. Kitchen shares a wall with an attached garage.

The inspection. Droppings about 1/4 in, pointed: mice. Concentrations behind the range, in the sink base at the back corner where the drain enters, and in the garage along the top of the foundation on the shared wall. A faint rub mark at a gap around the gas line where it passes from the garage into the kitchen, roughly 1/2 in: well over the 1/4 in a mouse needs. A runway shows in the dust under the range, coming out from beneath it and joining the wall at the cabinet end.

The sets.

• Garage, along the foundation top on the shared wall: two back-to-back pairs on the run, traps 1 to 4.
• Kitchen, at the range: a T where the runway from under the range meets the wall at the cabinet end, traps 5 to 7.
• Sink base, back corner: a single, trigger to the wall, trap 8, inside a tamper-resistant cover because the customer has a cat.
• Kitchen wall run toward the pantry: a back-to-back pair, traps 9 and 10.

10 traps, numbered and drawn on the sketch, small food baits, armed the first night. The gap at the gas line goes on the report as the entry point to seal, per 'Rodent Exclusion Materials and Opening Sizes'. Sealing around a gas pipe is done without levering on or bending the pipe; if it moves, or anyone smells gas, the work stops, everyone leaves the house, and the call goes to the gas utility from outside.

Next day. Catches: trap 2 (garage), trap 6 (T, the stem), trap 8 (sink base). Three mice. Traps 9 and 10 untouched, no new droppings near them.

Three days later. Catches: trap 3 (garage). One mouse. No new droppings in the kitchen. Traps 9 and 10 still untouched with no sign near them, so they move into the garage where sign continues.

The read. 4 mice over two checks, 3 then 1. Three of the 4 came from the garage run and the range T, which sits on the line between the gas line gap and the kitchen. That agrees with the inspection: they are coming from the garage through the gap. Trapping is removing the ones inside; sealing the gap is what stops the next ones, and the record says so.

Where trapping goes wrong

Traps baited heavily and set in open floor. Out of the runway, the trap is decoration.

Too few traps. A mouse population is cleared fastest by saturating the runways briefly, not by one trap left for weeks.

Setting traps where a cat or dog patrols without covers. A pet that learns the trap has food in it will find every one. Covered sets, or traps only behind appliances, until the pet is kept out.

Never moving a dead trap. A position that has caught nothing for a couple of checks, with no fresh sign, is telling you to move it.

Trapping instead of excluding. If catches keep coming at the same rate, animals are still coming in. Find the opening. The case in 'The Mouse Callback Traced to a Garage Door Corner' is what that looks like when the opening is one nobody thought to check.

References

• See related: Mouse and Rat Foraging Range and Trap Spacing
• See related: Rodent Exclusion Materials and Opening Sizes
• See related: Rodent Droppings and Hantavirus for the Trades
• See related: Pest Activity Signs Reference
• See related: The Mouse Callback Traced to a Garage Door Corner