1 - A caterpillar's sole responsibility is to eat and grow. Their appetites are so voracious that it is believed they consume and excrete up to 2,700 x their body size. Their bodies can grow to 100 x the size they are when they hatch. 

2 - Caterpillars can increase their body mass by 1000 x or more in a few weeks.

3 -  The first meal that a caterpillar usually eats is its own egg shell, which is rich in protein..

4 - Caterpillars have 12 tiny eyelets known as stemmata. 6 are located on each side of the head. These eyelets are arranged in a semi-circle from side to side on the head. Stemmata help to identify light and darkness. They do not result in good vision, as the caterpillar is unable to see images or visualize colors. Because of this, caterpillars move blindly from one place to another.

5 - Caterpillar's bodies have approx. 4,000 muscles in their bodies, with 1 or 2 neurons attached to each. (Human bodies have 629 muscles, grass hoppers have 900.
(A good number of the caterpillar's muscles are required because of their unique style of propulsion.)

6 - Caterpillars and butterflies both have 6 legs.

7 - Caterpillars move like waves, crawling from back to front in a wave motion.

8 - Caterpillars produce their own milk.

9 - Caterpillars chew their food with opposable toothed mandibles that can only be seen with a magnifying glass.

10 - Many caterpillars are poisonous due to the plants that they eat.   i.e. - Milkweed.

11 - Caterpillars go through a metamorphosis: egg, larva, pupa, and adult. Some turn into butterflies, others turn into moths, depending on the species.

12 - There are both poisonous and venomous caterpillars. Poisonous species will harm you if you touch, breath or consume them, whereas venomous species inject a toxin by a sting.

13 - Many caterpillar species, when infested with parasites, will resort to eating toxic plants to eliminate the parasites. While these toxic plants will retard the caterpillar's growth rate to a certain degree, they will successfully eliminate the parasites over time.

14 - Only the six legs found on a caterpillar's thorax are true legs, used for propulsion. The legs found on the abdomen are called prolegs, and have hooks that are used to help  climb and cling to leaf surfaces without slipping and falling. There can be up to 10 prolegs.

15 - Caterpillars produce silk through an opening on their lips known as the spinneret,  that releases liquid silk. Once the liquid contacts air, it sets into silk.

16 - The assassin caterpillar, (Lonomia obliqua), also known as giant silkworm moth, has caused many human deaths in South America, especially in Brazil. Its venom is relatively unknown, and under scientific research. Being stung by the assassin caterpillar 20 times or more, which can happen in seconds, can result in a person bleeding to death.

17 - When under potential threat of predation by birds, caterpillars will gather in  huge groups of up to 300, and arrange themselves to appear to be a snake, which, because of birds fear of snakes, is a deterent to this potential predation. 

18 - Caterpillars do not have lungs. Instead, they possess spiracles on each side of their bodies. These spiracles are connected to the trachea. Breathing oxygen and carbon dioxide respectively occurs during the movement of the caterpillar.

19 - No other animal moves like the caterpillar. Since they have no bones in their bodies, caterpillars move by squeezing their muscles in a wave-like motion.

20 - Many species of caterpillars use Thanatosis to protect themselves from predation.  (Thanatosis is the definsive maneuver where a caterpillar will play dead and remain motionless or drop to the ground in order to get the predator to leave them untouched.)

21 - In the Bible's Old Testament, caterpillars are feared as creatures that devour and destroy crops.

22 - Caterpillars must continually grow. Because of this, when they get too big for their skins they arch their backs to split their skins and shed them to make room for their next skins. They will shed four to five times before they pupate.

23 - Caterpillars often take on the colors of the leaves that they are eating, helping them to become camouflaged, and thus protecting them from predation.

24 - Caterpillars have setae (hair), that makes them particularly unpleasant for birds to swallow.

25 - Caterpillars use their waste secretions to bribe ants to become their body guards. Scientists have discovered that ants that consume the caterpillar's waste secretions become very aggressive against spiders that are trying to attack the caterpillars.

26 - Caterpillars are neither male or female. Their reproductive organs do not start to develop until they are inside the pupa. Thus caterpillars do not mate or reproduce. 

27 - Most caterpillars are nocturnal. They hide among plants during the day to protect themselves against daytime predators.

28 - Some moth caterpillars make cocoons. Butterfly caterpillars do not make cocoons, but make chrysalises instead. (They are easy to distinguish between because moth's cocoons are made of silk while butterflies' chrysalises are not.)

29 - Caterpillars have 248 individual muscles in their heads alone.

30 - Swallowtail (Papilio) caterpillars, if bothered, will give out a bright orange osmeteria from behind its head, which has a very foul odor.

31 - As a general rule, brightly colored caterpillars are toxic. Their bright colors are a reminder to predators of their toxicity.

32 - The wooly slug, also known as the puss caterpillar, is famous for spitting acid at its predators. It ia also the most poisonous caterpillar in the U.S.

33 - The majority of caterpillars are vegetarians, although some species will feed on caterpillars of other species.

34 - There are artic species of moths that spend 14 yrs. as caterpillars. They only become active for a few weeks every summer.

35 - Some caterpillars possess specialized underwater respiratory structures that enable them to survive in aquatic habitats. For example, the larvae of some pyralid moths (family Pyralidae) are aquatic, and several members of the genus Hyposmocoma (family Cosmopterigidae) have an amphibious caterpillar stage.

36 - A caterpillar's stomach is not attached to the side walls of the body, only the front and back. When the caterpillar moves, the stomach appears to move before the body walls do.

37 - Caterpillars move their mandibles from side to side to chew, unlike humans, who chew in an up and down motion.

38 - Caterpillars of the giant peacock moth (Saturnia pyri) send out ultrasonic warning chirps to deter predators. In some cases, those chirps occur just prior to or in conjunction with the release of pungent chemical deterrents. 

39 - The masked birch caterpillar (Drepana arcuata) produces vibratory signals in order to defend its territory against intruders of the same species; it produces the vibrations by drumming its mandibles on the leaf surface and by scratching its legs, which are covered by hairlike structures, against the leaf. 

40 - The Hickory Horned Devil is one of the largest caterpillars in the world. Fully grown, this horned caterpillar can grow up to 6” (15 cm). It transforms into one of the biggest moths in the world.

41 - There are approximately 180,000 species of caterpillars worldwide, of which approx. 20,000 have been identified.

42 - Caterpillars are typically in the caterpillar stage of their lives for about 3 wks.