Question: Which insect did Dali often use in his paintings, and what did they symbolize?
About the article "The Persistence of Memory", section "Description".

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Black and grey shades often symbolize gloom, fear, mystery, superstitions, evil, death, secret, sorrow.
The light source in most religious paintings symbolize hope, guidance or divinity.
In fantasy paintings light could symbolize magic. 
Crosfield's youthful oil paintings showed promise.
His interest in art was awakened by "Grassy" Feild, his art master at the Downs School, when he was 11.
By the age of 15 (around 1930) his landscape oils show the influence of Impressionism.
His father, himself an amateur painter, thought that his artistic talent and interest in engineering would best be served in architecture.
Marriage, the war, starting his own business and his growing family left little time for painting, but when he returned to it seriously, his art reflected the change in artistic values.
He was very interested in the development of abstract art and a frequent visitor to galleries.
He had seen a scanning electron microscope in a Helsinki research institute and, in 1975, when he had the money and the time to use it, he bought one from Cambridge Scientific Instrument Company.
Crosfield was to be seen in his painter's smock at the top of Grove Lodge (his birthplace, which he had bought in 1965) preparing, scanning and photographing minute objects - insect parts, pollen, petals, crystals - that he subsequently reproduced in colour and in a much larger scale on canvas.
Viewing nature magnified thousands of times "was like opening a door onto another planet."
Though he sponsored an exhibition at a West End gallery, he did not receive the recognition he hoped for, and he abandoned the subject but not painting itself.
He continued to paint landscapes, drawn from his extensive travels, and portraits, mainly for the family, until he packed up his paint box for the last time in April 2007, at the age of 91.
Though these later paintings demonstrated his technical skill and, given that he projected slides onto his canvas, were very realistic, they did not show the feel for his subjects that he had demonstrated as a boy nor the originality of the sometimes surreal paintings based on what he saw through the viewfinder of the electron microscope. 
Ernest Marc Louis de Gonzague Doudart de Lagrée (March 31, 1823 - March 12, 1868) was the leader of the French Mekong Expedition of 1866-1868.
He was born in Saint-Vincent-de-Mercuze near Grenoble, France, and graduated from the École Polytechnique.
He joined the navy and served in the Crimean War, then took up a post in Indochina in the hope that the climate would help his chronically ulcerated throat.
It did not, and throughout the Mekong expedition he was often in severe pain.
The expedition left Saigon on June 5, 1866.
In addition to his ulcers, Doudart de Lagrée suffered from fever, amoebic dysentery and infected wounds caused by leeches, as the expeditioners had to walk barefoot once they had worn out their supply of shoes.
By the time the expedition reached Dongchuan, in Yunnan, China, he was too sick to be moved, and his second-in-command Francis Garnier took command.
Garnier led the expedition to Dali, leaving Doudart de Lagrée in the care of the doctor.
He died from an abscess on his liver.
The doctor removed his heart to return it to France, while Doudart de Lagrée was buried in Dongchuan.
Ernest Doudart de Lagrée was also an entomologist.
Insect collections made by him in Africa are conserved in Muséum national d'histoire naturelle in Paris. 
In 863, a major Dali attack against Tang's Annan District (安南, headquartered in modern Hanoi, Vietnam) captured Annan, and the Tang protector general for Annan, Cai Xi (蔡襲), died while fighting the Dali forces.
They then approached Yong Prefecture (邕州, in modern Nanning, Guangxi), the capital for Lingnan West Circuit (嶺南西道).
The military governor of Lingnan West Circuit, Zheng Yu (鄭愚), who was a career civilian, was fearful of Dali forces and submitted a petition requesting to be replaced by a general.
Then-reigning Emperor Yizong (Emperor Xuānzong's son) recalled Kang to the capital Chang'an, intending to have him replace Zheng, and allowed him to bring several hundred officers and soldiers from Yiwu Circuit.
Upon Kang's arrival in Chang'an, Emperor Yizong commissioned him the military governor of Lingnan West, and also mobilized about 10,000 soldiers from Jingnan (荊南, headquartered in modern Jingzhou, Hubei), Shannan East (山南東道, headquartered in modern Xiangfan, Hubei), Eyue (鄂岳, headquartered in modern Wuhan, Hubei), and Jiangxi (江西, headquartered in modern Nanchang, Jiangxi) Circuits to accompany him to Lingnan West.
After Kang arrived at Yong Prefecture, the Dali attack was intensifying, so Emperor Yizong further mobilized troops from eight other circuits — Zhongwu (忠武, headquartered in modern Xuchang, Henan), Yicheng (義成, headquartered in modern Anyang, Henan), Pinglu (平盧, headquartered in modern Weifang, Shandong), Xuanwu (宣武, headquartered in modern Kaifeng, Henan), Yanhai (兗海, headquartered in modern Jining, Shandong), Tianping (天平, headquartered in modern Tai'an, Shandong), Xuanshe (宣歙, headquartered in modern Xuancheng, Anhui), and Zhenhai (鎮海, headquartered in modern Zhenjiang, Jiangsu) — to reinforce him.
Kang, however, did not set up a proper scouting system.
As Dali forces approached Yong Prefecture, Kang sent the troops from six circuits to engage them, using the local Liao (獠) tribesmen as guides; the Liao led the Tang forces into an ambush by Dali forces, and the troops of five circuits were annihilated, with only the Tianping forces, because they were late by one day, escaping the ambush.
In the aftermaths, Kang was gripped by fear, and the defenses for Yong Prefecture were actually built by his deputy Li Xingsu (李行素).
As soon as Li completed the defenses, Dali forces arrived and put Yong Prefecture after siege.
For four days, Yong Prefecture was under attack, and it almost fell.
A number of officers suggested counterattacking, but Kang initially refused, relenting only after repeated pleas by a low-level officer from Tianping.
At night, that Tianping officer took 300 volunteers and made a surprise attack on the Dali camp, setting it on fire and killing some 500 Dali soldiers.
In shock, the Dali forces withdrew.
Only then did Kang launch his main forces to try to chase down the Dali forces, but was unable to; they killed only some 300 Liao who were forced to cooperate with the Dali forces.
Kang nevertheless submitted a report claiming a great victory.
Emperor Yizong, in response, bestowed on Kang the honorific title of acting "You Pushe" (右僕射).
However, all of the soldiers who received rewards based on Kang's report were Kang's relatives or soldiers close to him, and the soldiers who participated in the surprise raid were not awarded.
This brought much resentment.
Subsequently, the military governor of neighboring Lingnan East Circuit (嶺南東道, headquartered in modern Guangzhou, Guangdong), found out what happened, and reported this to the chancellors.
Kang himself was fearful as well that his deception would be discovered, so he claimed to be ill and offered to resign.
He was recalled to serve as a general of the imperial guards, but with his office at the eastern capital Luoyang. 
Ryder completed fewer than two hundred paintings, nearly all of which were created before 1900.
He rarely signed and never dated his paintings.
Ryder used his materials liberally and without care.
His paintings, which he often worked on for ten years or more, were built up of layers of paint and varnish applied on top of each other.
He would often paint into wet varnish, or apply a layer of fast-drying paint over a layer of slow-drying paint.
The result is that paintings by Ryder remain unstable and become much darker over time; they crack readily, do not fully dry even after decades, and sometimes completely disintegrate.
Because of this, and because some Ryder paintings were completed or reworked by others after his death, many Ryder paintings appear very different today than they did when first created.
Many of his paintings suffered damage even during Ryder's lifetime, and he tried to restore them in his later years.