Malacosoma californicum pluviale 

Malacosoma californicum pluviale
Common name: northern tent caterpillar

Class: Insecta
Order: Lepidoptera
Family: Lasiocampidae

Host plants: broad-leaved deciduous hardwood trees

Adult size: moth wingspan = 1-1.5 in (2.5-3.8cm)
Larva size: length at last instar = 1.75-2.2 in (4.5-5.5cm)
Pupa size: 0.6 – 0.75 in (1.5-2.0cm)

Life cycle: one generation per year
                   egg – overwinter
                   larva – 5 to 6 instar stages lasting 6 weeks
                   pupation – 2 to 3 weeks
                   adult – 1 to 14 days


Description & Life Cycle: Young larvae emerge in spring coinciding with the leaves unfurling on hardwood trees. Timing is dependant on regional weather. Just an eighth of an inch long (3mm) and dark in colour, they are distinguishable by the white hairs covering their length.

For the next 6 weeks, the larvae eat their way through 5 to 6 instar stages, moulting out of their skin as they outgrow it. With each successive shedding, their distinguishable markings become visible. Down the centre of their back is a network of uniform orange patches, in the centre of which and corresponding to each body segment, is an elliptical light blue-grey patch outlined in dark brownish-black. There are two blue-grey dots in each body segment running down both sides beneath which runs a narrow orange strip. (Note: There can be variations in the markings.) By the end of the 5th or 6th instar stage, the caterpillars measure about 1.75 – 2.2 inches (4.5 – 5.5cm) long.

When they are ready to pupate at the end of the 6 weeks, the caterpillars spin cocoons of pale silk, covered in a yellow powdery dust, attached in a sheltered area of a tree or shrub. However, they will also use any convenient, out-of-the-way spot including up under the eave of the house or tool shed. The pupa is dark reddish-brown colour and measures 0.6 – 0.75 inches (1.5 – 2.0cm) long. In 14 – 21 days the adult moth emerges.

Stout-bodied adult moths vary in colour from buff yellow to a dark reddish-brown. Forewing is marked with a dark line running at a right angle from the body. Two paler lines run parallel to the outer wing edge and neatly divide the forewing into three equal segments. Wingspan ranges from 1.0 – 1.5 inches (2.5 – 3.8cm).

The moths do not feed and only live one to fourteen days. Their sole purpose is to mate. Once a female is fertilized, she lays 150 to 250 eggs in a sixth of an inch (1.5cm) long mass on a small diameter twig. She then encases them in spumaline – a frothy, glue-like substance which hardens and turns a glossy, dark brown colour. This protects the eggs from small predatory insects.

Within three weeks, the embryos have developed into phalate larvae. At this stage, they will diapause through the winter inside the eggs.



Special Notes: Malacosoma californicum pluviale are native to North America, more commonly found in the southern half of British Columbia as far east as Quebec and in Newfoundland. Their range also reaches south into the United States, typically west of the Cascade Mountains in Washington and Oregon states. But populations have also been found in the northern parts of Montana, Idaho and several northeastern states.

Young northern tent caterpillar larvae form a silky tent in the crotch of a tree branch, usually at the outer reaches of the tree crown…and there can be larvae from more than one egg mass within one tent. As the larvae grow in size, they increase the size of their silky tent.

Once they reach the last instar stage, the caterpillars begin to separate from the mass and start to search out suitable pupating spots.

Large outbreaks of northern tent caterpillars typically happen roughly every ten to twelve years and can last anywhere from three to six years in a row.

The adult moths are nocturnal and highly attracted to lights.



Natural Controls: Predators include frogs, small mammals and a large number of different bird species.

There are also a large number of insect predators including bees, wasps, flies, ants, beetles and earwigs that will prey on the northern tent caterpillar throughout various stages of its life span.

During large outbreaks numerous diseases are known to develop amongst colonies of Malacosoma species which can be directly attributed to controlling their numbers. One such disease is the nuclear polyhedrus virus, also known as nucleopolyhedrosis virus, or NPV. Often, an infected dead caterpillar will be seen hanging in place from a branch by its mid-section…its body forming an inverted V-shape.


Caution: The yellow powdery dust on the cocoon can cause an allergic reaction in some people.


Malacosoma californicum pluviale amongst M. disstriaIn our Zone 7a garden: We have been finding more of the forest tent caterpillars, related to the northern tent caterpillar, in our garden for the last three years now. (Check out the forest tent caterpillar here.)

However, it is not unusual to see the odd mature northern tent caterpillar intermingling with a mass of forest tent caterpillars as they search for a suitable spot to pupate.



Posted on May 31, 2013