VERTEBRATE PESTS: Neophobia, Neophilia and Hoarding

February 12, 2001

Most pest management professionals learn early in their rodent training of the terms neophobia and hoarding. But the word "neophilia" also surfaces from time to time regarding rodent behavior around our buildings, traps and bait stations. Let’s examine these interesting terms and how they fit into rodent behavior a bit closer.

Neophobia. The avoidance of strange objects, foods, areas and individuals of the same or different species is common among rodents (and other animals). This behavior is called neophobia (fear of new). All three species of commensal rodents exhibit levels of neophobic behavior, although rats in general tend to exhibit more neophobic tendencies than mice.

Many factors influence neophobic behaviors. If a rodent colony’s environment remains constant for long periods of time and food and water resources are abundant, any sudden changes in their living space may be met with caution — at least until the rodent re-habituates to the changes. Thus, to a certain degree, neophobic behavior serves as a survival strategy. A new box with a hole (e.g., a bait station) that suddenly appears in a rodent’s runway may initially be approached cautiously. Some mice will never enter curiosity traps or approach snap traps. These mice (or rats) are referred to as trap-shy.

The opposite behavior of neophobia is neophilia (new loving). Just as we have many examples of phobias, we also have many examples of "philias." Consider audiophiles (music lovers), bibliophiles (book lovers), soccerphiles, etc. Sometimes it is stated that certain rodents exhibit neophilic behavior (i.e., the rodents are attracted towards new items and areas).

For example, although some mice may exhibit neophobia, most mice are referred to as "curious" when they approach new traps and bait stations. That is, it is assumed they are attracted to the new objects in their territories and want to investigate them. However, it’s not this simple. In fact, neophilia behavior among rodents in the field (i.e., not in labs) is somewhat difficult to demonstrate compared to neophobic behavior. To consider whether rodents may be neophilic we need to first look at hoarding.

Hoarding. Hoarding is the collection and storing of items by animals. Many different animals (including people) exhibit hoarding tendencies. Hoarding behavior is also complex and dependant upon various population dynamics and local environmental factors. These factors, as well as others, influence whether or not a rodent will hoard an item or food, which items, quantities and whether or not the item will ever be eaten or used.

The house mouse, the Norway rat and the roof rat all exhibit hoarding behaviors. Many reports exist from professionals in the field of the types of foods and items that have been discovered in walls, cabinets and other areas as a result of hoarding behavior of commensal rodents. Hoarding obviously is the behavior that causes rodents to collect and move our baits around. In response, we as professionals have learned the importance of using block formulations and securing them to prevent rodents from translocating the poisonous foods to other areas.

Deer mice and white-footed mice seem to have strong hoarding tendencies. Some time ago, in my own attic, I noticed during some cleaning and renovating that about 12 different shaped and colored wooden pegs of a board game had all disappeared from the game’s box. My wife and I thought the pieces fell out of the box somewhere. We put the game aside figuring we’d find the pegs eventually as we cleaned up the attic. Only months later when pulling up some floor boards for renovation did I find a pile of the game pegs next to a large deer mouse nest in the attic’s floor void. What did the deer mouse want with the game pieces?

A more significant case occurred when my friend uncovered within a wall void two full matchbooks, several wooden matches, cotton yarn and several coffee filters. The heads of the matches showed clear impressions of the mouse’s incisors. It’s obvious how close my neighbor’s beautiful home came to disaster. The hoarding behavior of this deer mouse could have cost this family their home and maybe even their lives.

neophilic hoarding. Some rodent species of pest significance seem to be "neophilic" in their selection of which materials they hoard. Consider the woodrats of the genus Neotoma. Woodrats are also appropriately referred to as packrats and traderats. As their name implies, packrats collect many different items they encounter during their nightly forays and pack them away in a hidden spot or their nest. Nearly any new object they chance upon and can carry may be gathered, but they seem to be particularly attracted towards objects that are bright or shiny — it may be that shiny objects at night reflect glints of moonlight or other light and catch the rodent’s searching eyes during their routine foraging. Thus, packrats collect pieces of glass from broken bottles, pop-top tabs, aluminum cans, bottle caps, mirrors, spent ammo cartridges and the like. Accumulations of their collected items, both natural and man-made, may be stored in specific locations called "middens."

The natural items that have been found in middens include seeds, acorns, leaves, sticks, stems, bird feathers and pieces of bark of nearby trees. Also, snail shells, turtle shells and the bones and skulls of all different animals are common in middens. These shells and bones are gnawed upon, assisting the rats in sharpening their teeth. The bones are also frequently consumed — presumably allowing the rats to acquire calcium for their diet.

The human objects that have been found in outdoor packrat middens are numerous. For example, the following was discovered in one midden of an Eastern woodrat (Neotoma floridana): cans, glass, charcoal, bones, shells and bones of dead animals, cardboard boxes, cigarette butts, candy wrappers, rubber bands, shell casings and shotgun shells, metal, twist ties and aluminum pop tops. It’s as if we could use the Neotoma as an "indicator species" as to the careless habits of Homo sapiens that have passed through the wilderness and open spaces of Earth.

But this behavior is not restricted to packrats in the wild. Some current packrat pests of the West and Southwest frustrate homeowners. This is because packrats move into houses and cabins and periodically "steal" various household items they encounter including paper money, coins and jewelry. Pack rats are also called "trade-rats" because when they encounter keys, jewelry and various shiny utensils left on tables or next to sleeping bags, they drop whatever they are carrying at the time and pick up the new "attractive" object. In this manner, sticks have been traded for car keys, berries for wedding bands and so forth. Yet, are these rats "neophilic" in their hoarding behavior? That is, do they have a true attraction toward new objects over old objects?

Research has shown that even rodents with plenty of food continue to collect food items and store them in various areas, never to be eaten. Other items (i.e., twigs and pebbles) are collected over and over. Thus, it is likely these collections are opportunistic behaviors of gathering, storing and distributing as food reserves and other potential resources (nesting materials, calcium sources, etc.) in the territory for possible times of shortage or intense competition from other rodents. Such behaviors may also play a role in why rodents persist and re-populate buildings even in cases of massive clean-ups where we claim the food sources of the rodents are "removed." But there may be secret middens of food and materials some rats can still access and use for survival and reproduction after human clean-ups.

conclusion. In summary, rodents may exhibit both fear and attraction towards the various items they encounter in their daily travels and explorations. And some items may be collected and stored over and over again. Why some rodents collect certain items may have purpose or may be wasted energy. Why rats carry home shiny pebbles and drop them around their nest is anyone’s guess. But then I think of aliens visiting Earth and observing how we humans collect empty seashells and put them in jars that inevitably end up in forgotten attics. Perhaps they would ask, "What’s with that?"

The author is president of RMC Pest Management Consulting and can be reached at 765/939-2829 or rcorrigan@pctonline.com