What is caltrop?

A caltrop (also known as caltrap, galtrop, cheval trap, galthrap,[1] galtrap, calthrop, jackrock or crow's foot[2][3]) is an area denial weapon made up of two or more sharp nails or spines arranged in such a manner that one of them always points upward from a stable base (for example, a tetrahedron). Historically, caltrops were part of defences that served to slow the advance of troops, especially horses, chariots, and war elephants, and were particularly effective against the soft feet of camels.[4] In modern times, caltrops are effective when used against wheeled vehicles with pneumatic tires.

The modern name "caltrop" is derived from the Old English calcatrippe (heel-trap),[5][6] such as in the French usage chausse-trape (shoe-trap). The Latin word tribulus originally referred to this and provides part of the modern scientific name of a plant commonly called the caltrop, Tribulus terrestris, whose spiked seed cases resemble caltrops and can injure feet and puncture bicycle tires. This plant can also be compared to Centaurea calcitrapa, which is also sometimes referred to as the "caltrop". Trapa natans, a water plant with similarly shaped spiked seeds and edible fruit, is called the "water caltrop".

The caltrop was called tribulus[7] by the ancient Romans, or sometimes murex ferreus,[8] the latter meaning "jagged iron" (literally "iron jagged thing"). The former term derives from the ancient Greek word tribolos meaning three spikes.[9] Caltrops were used in the Battle of Carrhae in 53 BC.[10]

The late Roman writer Vegetius, referring in his work De re militari to scythed chariots, wrote:[11]

Another example of the use of caltrops was found in Jamestown, Virginia, in the United States:[12]

The Japanese version of the caltrop is called makibishi. Makibishi were sharp spiked objects that were used in feudal Japan to slow pursuers and also were used in the defence of samurai fortifications. Iron makibishi were called tetsubishi, while the makibishi made from the dried seed pod of the water caltrop, or water chestnut (genus Trapa), formed a natural type of makibashi called tennenbishi. Both types of makibishi could penetrate the thin soles of shoes, such as the waraji sandals, which were commonly worn in feudal Japan.[13][14]

Punji sticks perform a similar role to caltrops. These are sharpened sticks placed vertically in the ground. Their use in modern times targets the body and limbs of a falling victim by means of a pit or tripwire.[citation needed]

During the Second World War, large caltrop-shaped objects made from reinforced concrete were used as anti-tank devices, although it seems that these were rare.[15] Much more common were concrete devices called dragon's teeth, which were designed to wedge into tank treads. Large ones weighing over 1 tonne (1.1 tons) are still used defensively to deny access to wheeled vehicles, especially in camp areas. As dragon's teeth are immobile, the analogy with the caltrop is inexact. Another caltrop-like defence during World War II was the massive steel, freestanding Czech hedgehog; the works were designed as anti-tank obstacles, and could also damage landing craft and warships that came too close to shore. These were used by the Germans to defend beaches at Normandy and other coastal areas.[16] Czech hedgehogs are heavily featured and plainly visible in the 1998 Steven Spielberg-directed American epic war film Saving Private Ryan, throughout the scenes early in the film depicting the June 6, 1944 Omaha Beach assault (part of the Normandy landings during World War II).

Tetrapods are concrete blocks shaped like caltrops, which interlock when piled up. They are used as riprap in the construction of breakwaters and other sea defences, as they have been found to let the water pass through them and interrupt natural processes less than some other defenses.[citation needed]

Researchers have tried to develop a caltrop-like device to deflate vehicle tires in a manner useful to law enforcement agencies or the military.[17][18]

During service in World War I, Australian Light Horse troops collected caltrops as keepsakes. These caltrops were either made by welding two pieces of wire together to form a four-pointed star or pouring molten steel into a mould to form a solid, seven-pointed star. The purpose of these devices was to disable horses. They were exchanged with French troops for bullets. The Australian Light Horse troops referred to them as "Horse Chestnuts".[citation needed]

Caltrops were used extensively and effectively during World War II. The modifications and variants produced by the Special Operations Executive (SOE) and the Office of Strategic Services (OSS) of the United States[19] are still in use today within special forces and law enforcement bodies.[who?]

The Germans dropped crow's feet (German: Krähenfüße).[20] These were made from two segments of sheet metal welded together into a tetrapod with four barbed points and then painted in camouflage colours. They came in two sizes with a side length of either 65 or 75 millimetres (2.6 or 3.0 in). They were dropped from aircraft in containers the same size as a 500 kg bomb and were dispersed by a small explosive charge.[20][21]

Caltrops have been used at times during labour strikes and other disputes. Such devices were used by some to destroy the tires of management and replacement workers.

Caltrops, referred to as "jack rocks" in news articles, were used during the Caterpillar strike in 1995, puncturing tires on vehicles crossing the picket line in Peoria, Illinois. Because of their small size and the difficulty proving their source, both the company and the United Auto Workers blamed each other. Collateral damage included a school bus and a walking mail carrier.[22] In Illinois, the state legislature passed a law making the possession of such devices a misdemeanor.[23][24]

A caltrop has a variety of symbolic uses and is commonly found as a charge in heraldry.[25] For instance, the Finnish noble family Fotangel (Swedish for 'caltrop') had arms gules, three caltrops argent.

It has also been adopted by military units: the caltrop is the symbol of the US Army's III Corps, which is based at Fort Hood, Texas. III Corps traces its lineage to the days of horse cavalry, which used the caltrop as a defensive area denial weapon.

The caltrop is also the symbol of the United States Marine Corps' 3rd Division, formed on 16 September 1942.[citation needed]

The Savannah Association annually commemorate Operation Savannah, a battle from 1975 to 1976 in the South African Border War (also known as the Namibian War of Independence). The battle involved a covert intervention by the South African Defence Force (SADF) during the Angolan War of Independence, subsequent Angolan Civil War and Namibian War of Independence. During this battle many South African soldiers earned the Honoris Crux for bravery against Angolan and Cuban forces. Their insignia was a caltrop.

Caltrop (Tribulus terrestris) is a summer-growing weed found widely throughout Western Australia. It is most common in areas of frequent spring and after summer rain.

Under the Local Government Act 1995 it is a prescribed pest plant in a number of shires in the Perth metropolitan area, the southwest and the wheatbelt.

However it is not a declared plant, and there is no requirement to report it to the Department of Agriculture and Food, Western Australia.

Caltrop has seeds that remain dormant in the soil for probably four to five years. They germinate after summer rain. Plants grow rapidly, flowering and forming new burrs within three to five weeks.

The trailing stems of caltrop are long and wiry. They are covered with fine hairs. The stems lie prostrate on the ground, radiating from a central taproot. The leaves consist of several leaflets arranged opposite each other on the stems. The leaves are fern-like and greyish-green. Caltrop is often confused with doublegee; however, the latter has a green leaf similar to English spinach.

The flowers are small, less than 1cm in diameter, and yellow with five petals. Wedge-shaped burrs are formed in clusters of five, each with four or more long sharp spines.

Under cropping situations the weed is of little agricultural importance as it is a summer-growing plant, which does not affect winter crops. Sheep readily eat it, but there have been a number of confirmed cases of caltrop poisoning in sheep and goats. Caltrop is a nuisance around farm buildings, townsites, railway yards, roadsides, car parks, cycle paths and other recreation areas because of the sharp spiny burrs.

A heavy infestation after summer rain can produce an abundance of spiny burrs, which make it very uncomfortable for people and animals alike.

Small numbers of plants can be eliminated by hand grubbing. The plants may be placed in a bag and disposed of in a bin or they could be dried and then burnt, if permitted by local council bylaws.

The recommended method of control for small infestations on farms is 2,4-D amine (625g/L) at the rate of 2.5mL/L of water in a knapsack sprayer and 2.4L/ha of 2,4-D amine for large paddock infestations. Often further treatment for new germinations is necessary after each summer rainstorm.

Under very warm/dry conditions the addition of a crop oil may improve the result.

*Other formulations available and rates should be adjusted when using these. # Where a rate of herbicide is specified as an upper or lower rate, that is, 11–25mL or 1.1–2.4L the lower rate should be used for seedlings and juvenile plants. The upper rate should be used for mature or flowering plants.

Considerable care must be taken when selecting and applying chemicals in townsites and/or where vines, tomatoes and other vegetable crops are grown commercially because some are unsuitable for use in these situations.

The proximity of gardens, and vegetable or vine crops makes the use of 2,4-D and other hormone type herbicides inadvisable. This is because of the possibility of herbicide drift either as droplet or vapour. The drift of all herbicides can also be of concern if the application is made under unfavourable conditions such as high temperatures, too low or too high wind speeds, and under conditions where temperature inversions occur trapping vapour and droplets and moving the herbicide considerable distances. The topic of herbicide drift is covered in other publications.

Where applied on house blocks near trees or in areas to be used for gardens the non-residual foliar herbicides should be used. In these areas, Reglone® or glyphosate may be the best option for control.

In this situation regular inspections will have to be made to determine if other germinations of caltrop have occurred, which will then need treating.

To prevent spread of the weed, tyres and footwear should be cleaned to remove burrs.

*Other formulations available and rates should be adjusted when using these. # Where a rate of herbicide is specified as an upper or lower rate, that is, 11–25mL or 1.1–2.4L the lower rate should be used for seedlings and juvenile plants. The upper rate should be used for mature or flowering plants.