Rats and mice are the most diverse group of rodents worldwide. They are characterized by having a single pair of sharp, ever-growing incisors in the upper and lower jaws, coupled with the absence of canine teeth. They are also the most successful group of animals, as revealed by their agile burrowing, climbing, jumping and swimming abilities. They are also prolific breeders with acute hearing, smelling and touch senses. They also possess keen memory on the surrounding environments. All these abilities have enabled them to survive in a broad range of habitats.
Whilst a majority of rats and mice thrive in the natural environments, some species have adapted to the human settlements, causing nuisance to the human populations. The major harms caused by these commensal rodents, or rodent pests, include:
1.
Economic losses and illnesses caused by their consumption and contamination of our field crops and stored foods.
2.
Economic and property losses caused by their burrowing and gnawing habits.
3.
Fire hazards resulted from their gnawing on electric wires and cables.
4.
Health risks to humans as they, along with the associated ectoparasites, are hosts or vectors of various kinds of communicable diseases.
In Hong Kong, there are three species of rodent pests commonly found in the urban environments: the Norway rat or sewer rat (Rattus norvegicus), the roof rat (Rattus rattus), and the house mouse (Mus musculus). The following table summarizes the identification details of these three rodent pests:
Norway Rat
Roof Rat
House Mouse
Adult size
Large (about 32-47cm from the head to the tip of the tail)
Medium (about 27-43cm from the head to the tip of the tail)
Small (about 7-20cm from the head to the tip of the tail)
Adult weight
200-450g
120-225g
15-30g
Head
Small in proportion to body;
Blunt nose and muzzle
Large in proportion to body;
Pointed nose and muzzle
Large in proportion to body;
Pointed nose and muzzle
Ears
Small. Do not cover eyes when pulled forward
Large. Cover eyes when pulled forward
Large. Cover eyes when pulled forward
Eyes
Small
Large
Large
Tail
Shorter than head-and-body length;
Thick with paler underside
Longer than head-and-body length;
Uniformly dark
Slightly shorter or longer than head-and-body length;
Scaly with uniform greyish-brown colour
Body
Stocky with brown / grey / dark fur;
Belly colour varies from grey to pale brown
Slender with uniform greyish-brown / dark fur;
Belly colour varies from grey to creamy-white
Small and slender with brown / greyish brown fur;
Belly colour similar
Droppings
Large (~1.9 cm) and capsule shaped
Small (~1.3 cm) and spindle shaped
Small (~0.3 cm) and rod shaped
Habits
Agile swimmer that climbs less frequent than other rats;
Ground dwelling, often nests in burrows;
Also inhabit underground sewers;
Nocturnal
Agile climber that rarely swims and burrows;
Frequents overhanging structures such as attics, false ceilings, roof spaces, and crossbeams of the buildings;
Nocturnal
Agile climber;
Usually found indoors particularly around food storage;
Nocturnal but also moderately active during daytime
Prevention and Control
The most fundamental and effective way of rodent prevention and control is to eliminate the food, harbourage and passages for the pest. This can be achieved via proper handling of refuse, storage of food, and keeping of articles. Blockage/ elimination of rodent passages through installation of gratings, wire mesh or metal plates etc. are structural rodent-proofing measures essential for successful rodent disinfestation with rodenticides or trapping.
To facilitate the planning of rodent prevention and control strategies, the Pest Control Advisory Section (PCAS) of Food and Environmental Hygiene Department (FEHD) has been conducting routine, territory-wide Rodent Infestation Survey to monitor the rodent problem in different areas since 2000. Rat-flea Surveys have also been conducted at the port areas and areas with different environmental conditions in the community to assess the risk of local plague transmission. To enhance the public alert on rodent prevention, and to enlist support from the community in controlling rodents, territory-wide interdepartmental Anti-rodent Campaign is held every year. Meanwhile, FEHD also carries out regular anti-rodent operations at strategic locations over the territory.
Further information on rodent prevention and control/ 2006 Anti-rodent Campaign can be obtained from other pages of the FEHD official website. (http://www.fehd.gov.hk/safefood/Pcasc.html)
Rattus norvegicus
Rattus norvegicus
Rattus rattus
Mus musculus
Droppings of Rattus norvegicus
Droppings of Rattus rattus
Droppings of Mus musculus
Poor environmental hygiene is prone to rodent infestation
Rodent-proofing measures are crucial for successful rodent prevention and control
Differences between Mosquitoes and Biting Midges
Both biting midges and mosquitoes are frequent biters of humans and other vertebrates. Biting midges are very often mistaken for mosquitoes by people complaining insect bites. In this issue, the biology and medical importance of biting midges and mosquitoes are compared to illustrate their similarities and differences.
White or yellowish when laid (but turn black later)
Larva
Aquatic;
with distinct body regions
Aquatic or semi-aquatic;
without distinct body regions except for the head
Adult size
About 2-10 mm long;
About 1-4 mm long; (about half of the body size of an adult mosquito visually)
Adult morphology
Long and slender body;
long legs;
long proboscis
Robust body;
short and stout legs;
short proboscis
Adult female
With piercing and sucking mouthpart; most are blood-feeding
With piercing and sucking mouthpart;
some are blood-feeding
Flight ability
Usually strong flier (can be up to 2 km from the breeding site)
Usually weak flier (usually less than 100 m from the breeding site)
Medical Importance
Regarded as important human disease vector which can transmit diseases like malaria, dengue fever, Japanese encephalitis;
cause irritation through bites
Generally not regarded as an important human disease vector, though some can transmit parasite and virus to humans;
cause irritation through bites
Prevention and control
Breeding of the insect can be avoided by prevention of stagnant or slow flowing water from the access of adult mosquitoes;
insect can be killed by application of insecticide.
Keeping the soil surface dry and avoiding accumulation of decaying vegetation can prevent breeding of the insect;
regular trimming of densely grown vegetation would help to keep the soil surface dry and reduce the resting places of the insect;
insect can be killed by application of insecticide.
Last revision date: 03-07-2006